API: Extracted routing functionality into a router class.
API: Consistently named http request methods.
API: Move SS_HTTPRequest::send_file() into the HTTP class.
API: Change the way requests are constructed, and include server vars.

* Environment variables (get, post, files and server vars) are now
  passed in as an associative array to the constructor.
* Add methods for accessing server variables on the request.
API: Make HTTP headers case insensitive.
Move header extraction to the request class.
Move method detection to the request class.
Move the overriding of superglobals into SS_HTTPRequest->setGlobals().
API: Add basic auth methods to the request object.
Update basic auth test for request global changes.