Merge pull request #2 from avsm/master

Fixes for latest mirage-types, using read instead of listen
Merge pull request #3 from avsm/master

release 0.9.0
Merge pull request #4 from avsm/master

fixes for mirage types 0.5.0
travis: test on 4.x ocaml only
Depend on the unified io-page library instead of io-page-unix