HTTP message and parser improvements:
* 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
HTTP(S)-RPC server improvements (RIPD-489, RIPD-533):
* Correct handling of Keep-Alive in socket handlers
* Report session history in print command
Set version to 0.26.3-rc3