CP-17 Gzip/deflate support for asset requests

Support for requests that have content-encoding set to gzip or deflate regardless
of collapsify not setting the relevant accept-encoding header.
CP-18 Support for media type in link tag.

The mediatype defined in the media attribute of the link tag was not being inlined.
The inlined stylesheet is now wrapped by  @media mediatype {}.
The svg+xml mimetype was added to the list of supported mimetypes.
Merge pull request #1 from cloudflare/cp-17

Add support for zipped streams and media queries.