update .merlin

* keep up with the cohttp -> lib rename
* add cmdliner
simplify expression in bin/lwt_server
Lwt_unix.run is deprecated

Lwt_main.run should be used
Merge pull request #216 from rgrinberg/merlin_update

Merlin update
Merge pull request #217 from rgrinberg/remove_lwt_unix_run

Remove Lwt_unix.run