This changes the HTTP parser interface to return an error_code instead
of a bool. This eliminates the need for the error() member function and
simplifies calling code.
* streambuf wrapper supports rvalue move
* message class holds a complete HTTP message
* body class holds the HTTP content body
* headers class holds RFC-compliant HTTP headers
* basic_parser provides class interface to joyent's http-parser
* parser class parses into a message object
* Remove unused http get client free function
* unit test for parsing malformed messages