ResponseBody: Proper parsing of Content-Type header
ResponseBody: Proper parsing of Content-Type header

We've been ignoring the standard (RFC 2068) for a while now, instead
expecting every media-type to include a charset parameter (and only
that). Now, we corectly handle multiple, varied media-type parameters,
giving our media-type handlers that much more flexibility.

getContentType removed, superseded by parseContentType

new method parseContentType
    - Stores self.mediatype
    - Stores self.ctypeParameters, a dict of the parameters
    - Sets charset correctly, even if it was implicit, so the handler's
      don't have to implement any "default logic" for it

mozilla/agithub,jpaugh/agithub