doc (loader.md): Add missing English translations (eggjs#2996)

1) Add missing English translations about the explainations of start
process in details.
2) Format some words in a beautiful style.

History.md

@@ -5,7 +5,7 @@
 ### Notable changes
 
 * **feature**
-  * support boot lifecyle, see https://github.com/eggjs/egg/issues/2520
+  * support boot lifecycle, see https://github.com/eggjs/egg/issues/2520
   * `dnshttpclient` now use async function instead of Promise
 
 * **fix**
@@ -50,7 +50,7 @@
   * use cache-content-type
 
 * **docs**
-  * add lifecyle doc
+  * add lifecycle doc
   * add sequelize guide
   * add allowDebugAtProd in document
   * egg-scripts support windows

docs/assets/lifecycle_en.puml

@@ -0,0 +1,131 @@
+@startuml
+start
+: start master;
+partition agent {
+  : fork agent worker;
+  : load plugin.js, config.js, extends;
+  : load agent.js;
+  note right
+    class mode
+    configDidLoad
+    async didLoad
+    async willReady
+    async didReady
+    async serverDidReady
+    ====
+    method mode
+    beforeStart(deprecate)
+  end note  
+  fork
+  : configDidLoad;
+  note left
+    all the files are loaded
+    To execute some sync logic
+  end note
+  : async didLoad;
+  note left
+    Files and configs are loaded
+    To execute some async tasks
+    E.g: Pull configs in async to load client,
+    or check the state of client
+  end note
+  fork again
+    : beforeStart(deprecate);
+    note right
+      Tasks mounted on beforeStart
+      Running in parallel at this time
+    end note  
+  endfork
+  : async willReady;
+  note left
+    All the plug-ins are loaded,
+    All the plug-ins are normal,
+    To execute some tasks before request enters,
+    E.g: Pull some configs for applications
+  end note
+  : async didReady;
+  note right
+    agent is ready,
+    and it can work normally
+    ====
+    The time is the same as 'ready',
+    The original 'ready' doesn't support AsyncFunction    
+  end note
+  : emit 'agent-start';
+}
+partition app {
+  : start app workers;
+  : load plugin.js, config.js, extends;
+  : load app.js;
+  note right
+    class mode
+    configDidLoad
+    async didLoad
+    async willReady
+    async didReady
+    async serverDidReady
+    ====
+    method mode
+    beforeStart(deprecate)
+  end note
+  fork
+    : configDidLoad;
+    note left
+      All the files are loaded,
+      The same sync logic as in app.js,
+      Some configs can be modified, the order of middlewares
+    end note
+    : load app/service;
+    : load app/middleware;
+    : load app/controller;
+    : load app/router.js;
+    : async DidLoad;
+  note left
+    Files and configs are loaded
+    To execute some async tasks
+    E.g: Pull configs in async to load client,
+    or check the state of client
+  end note
+  fork again
+    : beforeStart(deprecate);
+    note right
+      Tasks mounted on beforeStart
+      Running in parallel at this time
+    end note
+  end fork
+    : async WillReady;
+  note left
+    All the plug-ins are loaded,
+    All the plug-ins are normal,
+    To execute some tasks before request enters,
+    E.g: Pull some configs for applications
+  end note
+  : async DidReady;
+  note right
+    app is ready
+    HTTP server starts listening at the port
+    ====
+    The time is the same as 'ready',
+    The original 'ready' doesn't support AsyncFunction
+  end note
+  : emit 'app-start';
+}
+: emit 'egg-ready';
+: async serverDidReady;
+note right
+  agent and all the apps are ready
+  requests are allowed
+end note
+: master receive SIGTERM;
+fork
+: agent beforeClose;
+fork again
+: app beforeClose;
+note right
+  To execute in a reversed order against the inserting
+  DO NOT recommend in PROD env,
+  May not finish before the process ends
+end note
+endfork
+stop
+@enduml

docs/source/en/advanced/loader.md

@@ -182,6 +182,82 @@ Note:
 - Same name will be override in loading, for example, if we want to override `ctx.ip` we could define ip in application's `app/extend/context.js` directly.
 - See [framework development](./framework.md) for detail application launch order.
 
+### Life Cycles
+
+The framework has provided you several functions to handle during the whole life cycle:
+
+- `configDidLoad`: When all the config files are loaded.
+- `didLoad`: When all the files are loaded.
+- `willReady`: When all the plug-ins are ready.
+- `didReady`: When all the workers are ready.
+- `serverDidReady`: When the server is ready.
+- `beforeClose`: Before the application is closed.
+
+Here're the definations:
+
+```js
+// app.js or agent.js
+class AppBootHook {
+  constructor(app) {
+  }
+
+  configDidLoad() {
+    // Config, plugin files have loaded.
+  }
+
+  async didLoad() {
+    // All files have loaded, start plugin here.
+  }
+
+  async willReady() {
+    // All plugins have started, can do some thing before app ready
+  }
+
+  async didReady() {
+    // Worker is ready, can do some things
+    // don't need to block the app boot.
+  }
+
+  async serverDidReady() {
+    // Server is listening.
+  }
+
+  async beforeClose() {
+    // Do some thing before app close.
+  }
+}
+
+module.exports = AppBootHook;
+```
+
+The framework will automatically load and initialize this class after developers have defined `app.js` and `agenet.js` in the form of class, and it will call the corresponding methods during each of the life cycles.
+
+Here's the image of starting process:
+
+![]( https://user-images.githubusercontent.com/6897780/45463932-bb1f9800-b740-11e8-9f0c-d9649ae8abc0.png)
+
+**Notice: We have an expiring time limitation when using `beforeClose` to close the processing of the framework. If a worker has accepted the signal of exit but doesn't exit within the limit period, it will be FORCELY closed.**
+
+If you need to modify the expiring time, please see [this document](https://github.com/eggjs/egg-cluster).
+
+Deprecated methods:
+
+## beforeStart
+
+`beforeStart` is called during the loading process, all of its methods are running in parallel. So we usually execute some asynchronized methods (e.g: Check the state of connection, in [`egg-mysql`](https://github.com/eggjs/egg-mysql/blob/master/lib/mysql.js) we use this method to check the connection state with mysql). When all the tasks in `beforeStart` finished, the state will be `ready`. It's NOT recommended to excute a function that consumes too much time there, which will cause the expiration of application's start.Plug-in developers should use `didLoad` instead, for application developers, `willReady` is the replacer.
+
+## ready
+
+All the methods mounted on `ready` will be executed when load ends, and after all the methods in `beforeStart` have finished executing. By the time Http server's listening also starts. This means all the plug-ins are fully loaded and everything is ready, So we use it to process some tasks after start. For developers now, we use `didReady` instead.
+
+## beforeClose
+
+All the methods mounted on `beforeClose` are called in an inverted order after `close` method in app/agent instance is called. E.g: in [`egg`](https://github.com/eggjs/egg/blob/master/lib/egg.js), we close logger, remove listening methods ...,ect.Developers SHOULDN'T use `app.beforeClose` directly now, but in the form of class to implement `beforeClose` instead.
+
+__We don't recommend to use this function in a PROD env, because the process may end before it finishes.__
+
+What's more, we can use [`egg-development`](https://github.com/eggjs/egg-development#loader-trace) to see the loading process.
+
 ### Loading File rules
 
 The framework will convert file names when loading files, because there is a difference between the file naming style and the API style. We recommend that files use underscores, while APIs use lower camel case. For examplem `app/service/user_info.js` will be converted to `app.service.userInfo`.

docs/source/zh-cn/advanced/loader.md

@@ -190,7 +190,14 @@ plugin1 为 framework1 依赖的插件，配置合并后 object key 的顺序会
 
 ### 生命周期
 
-框架提供了配置文件加载完成(`configDidLoad`), 文件加载完成(`didLoad`), 插件启动完毕(`willReady`), worker 准备就绪(`didReady`), 应用启动完成(`serverDidReady`), 应用即将关闭(`beforeClose`)这些生命周期函数。
+框架提供了这些生命周期函数供开发人员处理：
+
+- 配置文件加载完成（`configDidLoad`）
+- 文件加载完成（`didLoad`）
+- 插件启动完毕（`willReady`）
+- worker 准备就绪（`didReady`）
+- 应用启动完成（`serverDidReady`）
+- 应用即将关闭（`beforeClose`）
 
 定义如下:
 ```js
@@ -200,11 +207,11 @@ class AppBootHook {
   }
 
   configDidLoad() {
-    // Config,plugin files have did load.
+    // Config, plugin files have loaded.
   }
 
   async didLoad() {
-    // All files have did load, start plugin here.
+    // All files have loaded, start plugin here.
   }
 
   async willReady() {
@@ -234,26 +241,28 @@ module.exports = AppBootHook;
 
 ![](https://user-images.githubusercontent.com/6897780/42219323-24cbd7a8-7efe-11e8-86b9-cf280846aa9f.png)
 
-使用 `beforeClose` 的时候需要注意，在框架的进程关闭处理中是有超时时间的，如果 worker 进程在接收到进程退出信号之后，没有在所规定的时间内退出，将会被强制关闭。
+**使用 `beforeClose` 的时候需要注意，在框架的进程关闭处理中是有超时时间的，如果 worker 进程在接收到进程退出信号之后，没有在所规定的时间内退出，将会被强制关闭。**
+
 如果需要调整超时时间的话，查看[此处文档](https://github.com/eggjs/egg-cluster)。
 
 弃用的方法:
 
 ## beforeStart
-`beforeStart` 方法在 loading 过程中调用, 所有的方法并行执行。 一般用来执行一些异步方法, 例如检查连接状态等, 比如 [`egg-mysql`](https://github.com/eggjs/egg-mysql/blob/master/lib/mysql.js) 就用 `beforeStart` 来检查与 mysql 的连接状态。所有的 `beforeStart` 任务结束后, 状态将会进入 `ready` 。不建议执行一些耗时较长的方法, 可能会导致应用启动超时。
-插件开发者应使用 `didLoad` 替换。应用开发者应使用 `willReady` 替换。
+
+`beforeStart` 方法在 loading 过程中调用, 所有的方法并行执行。 一般用来执行一些异步方法, 例如检查连接状态等, 比如 [`egg-mysql`](https://github.com/eggjs/egg-mysql/blob/master/lib/mysql.js) 就用 `beforeStart` 来检查与 mysql 的连接状态。所有的 `beforeStart` 任务结束后, 状态将会进入 `ready` 。不建议执行一些耗时较长的方法, 可能会导致应用启动超时。插件开发者应使用 `didLoad` 替换。应用开发者应使用 `willReady` 替换。
 
 ## ready
+
 `ready` 方法注册的任务在 load 结束并且所有的 `beforeStart` 方法执行结束后顺序执行, HTTP server 监听也是在这个时候开始, 此时代表所有的插件已经加载完毕并且准备工作已经完成, 一般用来执行一些启动的后置任务。
 开发者应使用 `didReady` 替换。
+
 ## beforeClose
-`beforeClose` 注册方法在 app/agent 实例的 `close` 方法被调用后, 按注册的逆序执行。一般用于资源的释放操作, 例如 [`egg`](https://github.com/eggjs/egg/blob/master/lib/egg.js) 用来关闭 logger , 删除监听方法等。
-开发者不应该直接使用 `app.beforeClose`, 而是定义类的形式, 实现 `beforeClose` 方法。
 
-__这个方法不建议在生产环境使用, 可能遇到未执行完就结束进程的问题。__
+`beforeClose` 注册方法在 app/agent 实例的 `close` 方法被调用后, 按注册的逆序执行。一般用于资源的释放操作, 例如 [`egg`](https://github.com/eggjs/egg/blob/master/lib/egg.js) 用来关闭 logger , 删除监听方法等。开发者不应该直接使用 `app.beforeClose`, 而是定义类的形式, 实现 `beforeClose` 方法。
 
+__这个方法不建议在生产环境使用, 可能遇到未执行完就结束进程的问题。__
 
-可以使用 [`egg-development`](https://github.com/eggjs/egg-development#loader-trace) 来查看加载过程。
+此外，我们可以使用 [`egg-development`](https://github.com/eggjs/egg-development#loader-trace) 来查看加载过程。
 
 ### 文件加载规则