Added NewConnectionArgs()

Example:
```go
userType = types.NewGraphQLObjectType(types.GraphQLObjectTypeConfig{
		Name: "User",
		Fields: types.GraphQLFieldConfigMap{
			"id": gqlrelay.GlobalIdField("User", nil),
			"todos": &types.GraphQLFieldConfig{
				Type: todosConnection.ConnectionType,
				// Injects input fields into Relay connection args
				Args: gqlrelay.NewConnectionArgs(types.GraphQLFieldConfigArgumentMap{
					"status": &types.GraphQLArgumentConfig{
						Type:         types.GraphQLString,
						DefaultValue: "any",
					},
				}),
				Resolve: func(p types.GQLFRParams) interface{} {
					....
				},
			},
			...
		},
		Interfaces: []*types.GraphQLInterfaceType{nodeDefinitions.NodeInterface},
	})
```

connection.go

@@ -3,7 +3,7 @@ package gqlrelay
 import "github.com/chris-ramon/graphql-go/types"
 
 /*
- Returns a GraphQLFieldConfigArgumentMap appropriate to include
+Returns a GraphQLFieldConfigArgumentMap appropriate to include
 on a field whose return type is a connection type.
 */
 var ConnectionArgs = types.GraphQLFieldConfigArgumentMap{
@@ -21,13 +21,24 @@ var ConnectionArgs = types.GraphQLFieldConfigArgumentMap{
 	},
 }
 
+func NewConnectionArgs(configMap types.GraphQLFieldConfigArgumentMap) types.GraphQLFieldConfigArgumentMap {
+	for fieldName, argConfig := range ConnectionArgs {
+		configMap[fieldName] = argConfig
+	}
+	return configMap
+}
+
 type ConnectionConfig struct {
 	Name             string                      `json:"name"`
 	NodeType         *types.GraphQLObjectType    `json:"nodeType"`
 	EdgeFields       types.GraphQLFieldConfigMap `json:"edgeFields"`
 	ConnectionFields types.GraphQLFieldConfigMap `json:"connectionFields"`
 }
 
+type EdgeType struct {
+	Node   interface{}      `json:"node"`
+	Cursor ConnectionCursor `json:"cursor"`
+}
 type GraphQLConnectionDefinitions struct {
 	EdgeType       *types.GraphQLObjectType `json:"edgeType"`
 	ConnectionType *types.GraphQLObjectType `json:"connectionType"`

mutation.go

@@ -35,10 +35,16 @@ provided MutationConfig.
 func MutationWithClientMutationId(config MutationConfig) *types.GraphQLFieldConfig {
 
 	augmentedInputFields := config.InputFields
+	if augmentedInputFields == nil {
+		augmentedInputFields = types.InputObjectConfigFieldMap{}
+	}
 	augmentedInputFields["clientMutationId"] = &types.InputObjectFieldConfig{
 		Type: types.NewGraphQLNonNull(types.GraphQLString),
 	}
 	augmentedOutputFields := config.OutputFields
+	if augmentedOutputFields == nil {
+		augmentedOutputFields = types.GraphQLFieldConfigMap{}
+	}
 	augmentedOutputFields["clientMutationId"] = &types.GraphQLFieldConfig{
 		Type: types.NewGraphQLNonNull(types.GraphQLString),
 	}