add http_parser_module. The first working version, it can only parse header.
add docstring module.

   1. it includes `doc`, `doc_function`, `doc_constructor`, `doc_method`, `doc_module`, and `doc_module_mothed`.
   2. Use FunctionTemplate to create a object, instead of ObjectTemplate, then we can add documents to the constructor.
   3. rewrite the all tests so that it works in both debug mode and release mode. fix many small bugs that related with the release mode.
   4. Now C++ module and JavaScript module have same interface.
Update README.md