Expression 四则运算 (oceanbase#233)

### What problem were solved in this pull request?

Problem: close oceanbase#229 
当前的词法分析语法分析非常简单，那当遇到比较复杂的词法分析语法分析题目，比如表达式，有些同学就难以入手

### What is changed and how it works?
增加一个支持四则运算的功能，关键字是calc，虽然与标准的SQL不同，但是可以作为学习表达式入门使用。
使用示例：
```
(base) build_debug $ ./bin/observer -f ../etc/observer.ini -P cli
Successfully load ../etc/observer.ini
miniob > calc 2*(2*(2+3));
2*(2*(2+3))
20

miniob > calc (1+2) * (2 * (20+ -(5*1)))
(1+2) * (2 * (20+ -(5*1)))
90

miniob > calc 1, 2, 3;
1 | 2 | 3
1 | 2 | 3

miniob > calc 1 + 2 - 3+4;
1 + 2 - 3+4
4

miniob > calc 2* 4;
2* 4
8

miniob > calc 1, 2, 3;
1 | 2 | 3
1 | 2 | 3

miniob > calc 1 + 2 - 3+4;
1 + 2 - 3+4
4

miniob > calc 2* 4;
2* 4
8
```

Author: hnwyllmm

.github/ISSUE_TEMPLATE/feature_request.md

@@ -2,7 +2,7 @@
 name: Feature request
 about: Suggest an idea for this project
 title: ''
-labels: ''
+labels: feature
 assignees: ''
 
 ---

CMakeLists.txt

@@ -53,22 +53,16 @@ IF (CONCURRENCY)
     SET(CMAKE_COMMON_FLAGS "${CMAKE_COMMON_FLAGS} -DCONCURRENCY")
     ADD_DEFINITIONS(-DCONCURRENCY)
 ENDIF (CONCURRENCY)
-# test coverage
-SET(CMAKE_COMMON_FLAGS "${CMAKE_COMMON_FLAGS} -fprofile-arcs -ftest-coverage")
-SET(CMAKE_CXX_FLAGS ${CMAKE_COMMON_FLAGS})
-SET(CMAKE_C_FLAGS ${CMAKE_COMMON_FLAGS})
-MESSAGE(STATUS "CMAKE_CXX_FLAGS is " ${CMAKE_CXX_FLAGS})
 
 MESSAGE(STATUS "CMAKE_CXX_COMPILER_ID is " ${CMAKE_CXX_COMPILER_ID})
 IF ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
-  ADD_LINK_OPTIONS(-static-libgcc -static-libstdc++)
+    ADD_LINK_OPTIONS(-static-libgcc -static-libstdc++)
 ENDIF()
 
 IF (ENABLE_ASAN)
-    SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-omit-frame-pointer -fsanitize=address")
-    SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-omit-frame-pointer -fsanitize=address")
+    SET(CMAKE_COMMON_FLAGS "${CMAKE_COMMON_FLAGS} -fno-omit-frame-pointer -fsanitize=address")
     IF ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
-      ADD_LINK_OPTIONS(-static-libasan)
+        ADD_LINK_OPTIONS(-static-libasan)
     ENDIF()
 ENDIF()
 
@@ -106,9 +100,14 @@ ADD_SUBDIRECTORY(benchmark)
 ADD_SUBDIRECTORY(tools)
 
 IF(WITH_UNIT_TESTS)
+    SET(CMAKE_COMMON_FLAGS "${CMAKE_COMMON_FLAGS} -fprofile-arcs -ftest-coverage")
     enable_testing()
     ADD_SUBDIRECTORY(unittest)
-ENDIF()
+ENDIF(WITH_UNIT_TESTS)
+
+SET(CMAKE_CXX_FLAGS ${CMAKE_COMMON_FLAGS})
+SET(CMAKE_C_FLAGS ${CMAKE_COMMON_FLAGS})
+MESSAGE(STATUS "CMAKE_CXX_FLAGS is " ${CMAKE_CXX_FLAGS})
 
 INSTALL(DIRECTORY etc DESTINATION .
 		FILE_PERMISSIONS OWNER_WRITE OWNER_READ GROUP_READ WORLD_READ)