Implements inline compression for both gzip and brotli via the brotli
library. The library requires that Content-Type is set. The
implementation here explicitly avoids wrapping the ResponseWriter in
cases where Accept-Encoding is not set so as to maximally attempt to get
out of the way of hijack and upgrade concerns. It also avoids any
attempt at compression if Content-Encoding is already set so that
handlers that already perform compression are unaffected.
Signed-off-by: James Tucker <james@tailscale.com>
08a34edd91