get rid of \r\n in output from Cookies.render_*

This is a backward-incompatible change.

Now render_request defaults to what you'd normally want ("; ".join)
for a Cookie: header, while render_response returns a list of
the values you'd want for separate Set-Cookie headers (there is no safe
way of combining Set-Cookie headers without ambiguity, and it isn't
allowed in RFC 6265). The combine= parameter is no more.

By default, values are sorted to give more deterministic output.
Pass sort=False to skip this step (and let me know if it makes any
real performance difference for you).

This should be more versatile in general, more specifically friendly
to uses in a WSGI environment and should clean up the API guide some.
Generating raw HTTP responses is a less frequent requirement (e.g.
nobody much uses CGI now) and doing it from the new output is cleaner
than it was to do the usual cases by splitting strings, etc.