Add HTTP protocol and client support:
* New http::client_session for making requests
* Add 10,000 popular URL data set for unit tests
* Restructure joyent message parser (from Node.js):
  - New http::raw_parser wrapper
  - Convert parser errors to error_code
  - Enumeration and strings for parsed HTTP method
  - Move parser engine into joyent namespace
  - Rename includes to be distinct