Added a test case allow Accessing Subscripts of Optional Type
Allow let have no initializer within a type definition
Fixed when function's external name is not equal to argument label, it gives an incorrect compilation result
Make sure class's init's parameter always has an external name
Added syntax sugar for represent a dictionary type in parser
Unified the procedure to infer collection's element type for both Dictionary and Array
Added some interfaces for Dictionary type for unit test
Check subscript access is available during assignment
Added unary function support
Added test case ''Accessing Subscripts of Optional Type''
Implemented Chaining on Methods with Optional Return Values

Implemented Linking Multiple Levels of Chaining
Make tokenizer contextual sensitive
Added test cases for operators
Unified associated values and raw values for enum(New syntax updates)
Updated operator's syntax to new syntax
Allow GlobalScope to load standard library from external source file