Sprockets-mixins-mediatype

---------------------
- Add :func:`sprockets.mixins.mediatype.content.install`.
- Add :func:`sprockets.mixins.mediatype.content.get_settings`.
- Deprecate :meth:`sprockets.mixins.mediatype.content.ContentSettings.from_application`.
- Update to ietfparse 1.4.

----------------------
- Set the _`Vary` header if we are setting the content type.

----------------------
- Removed deprecation wrapper since it seems to cause really interesting
problems including the much feared meta-class error.

----------------------
- Repackage from a module into a package. Distributing raw modules inside
of a namespace package is unreliable and questionably correct.
- Add :func:`sprockets.mixins.mediatype.content.add_transcoder`.
- Add :class:`sprockets.mixins.mediatype.transcoders.JSONTranscoder`.
- Add :class:`sprockets.mixins.mediatype.transcoders.MsgPackTranscoder`.
- Add :class:`sprockets.mixins.mediatype.transcoders.BinaryWrapper`.
- Normalize registered MIME types.
- Raise a 400 status when content body decoding fails.

----------------------
- Support using the default_content_type in the settings if request does not
contain the Accept header

----------------------
- Update installation files