Refine `Vchan type, functorise mirage over Vchan

We change the `Vchan to int (* domid *) * Vchan.Port.t (* port *)
This matches the upstream convention. Note we also add a dependency
on vchan.

Signed-off-by: David Scott <dave.scott@citrix.com>
Lowercase filenames
Fix warnings
Add .merlin
Update opam
Compile on 4.01
Merge branch 'master' of github.com:samoht/ocaml-conduit

Conflicts:
	lib/conduit_mirage.ml
Update .merlin
Add the missing Vchan functions in conduit_lwt_unix
Add missing deps in travis
Install libxen-dev and uuid-dev in travis
Add mirage-dev remote earlier
Fix the build scripts to work with vchan

(also remove the Lwt syntax extension to speed up builds)
Use the new types for Vchan V1
Merge pull request #15 from samoht/master

Fixes