This changes the http::message object to no longer contain a body. It modifies
the parser to store the body in a separate object, or to pass the body data
to a functor. This allows the body to be stored in more flexible ways. For
example, in HTTP responses the body can be generated procedurally instead
of being required to exist entirely in memory at once.
* 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
