Add some module type equalities in cohttp_lwt_unix

This allows type Cohttp_lwt_unix.Server.Request.IO.ic to be Lwt_io.input_channel
Merge pull request #12 from chambart/master

Add some module type equalities in cohttp_lwt_unix
Merge branch 'master' of github.com:mirage/ocaml-cohttp
bump to 0.9.16 and sync Travis