Fix cases where the q-value is 0 and where a wildcard
was sent in the accept-charset header.
Also don't send a charset in the content-type of the
response if the media type is not text.
Thanks to Philip Witty for help figuring this out.
Also {switch_handler, Module, Opts}.
Allows switching to a different handler type. This is
particularly useful for processing most of the request
with cowboy_rest and then streaming the response body
using cowboy_loop.
