Added support for charsets on Content-Type headers. Fixes #37.

- Repurposed existing parser (previously AcceptComponent) and added logic
  for pulling out charset converting to .NET Encoding. Renamed this
  class MediaType.

- Changed ICodec to take a MediaType on the CanParse method.

- Updated codecs to test for encoding when determining whether or not they
  can serve a request.
Merge branch 'dev' of github.com:EventStore/EventStore into dev