Add errors:
- AmbiguousNewDeclarationError:
	Ambiguous new declarations
		with the same parameter list but different return values
- ConflictMainError:
	Multiple main functions
- MethodCallAmbiguousError:
	Ambiguous method matches the method call
- NoMatchMethodError:
	No method matches the call
- RedefinitionError:
	Redefine the same function
- VarOverrideMethodError:
	Try to override the method with a variable

Add CommonUtils:
- copyList: shallow copy a List

- Add symbol FunctionTable to store the overload table of a function
- Add function isFunctionTable in Symbol to check the type