Merge pull request #1165 from mlin/master

add new version of ocaml+twt, v0.93.2
+shared-memory-ring.0.4.2
+shared-memory-ring.0.4.3
+mirage.0.9.7
bump mirage-www constraints to reflect mirage.0.9.7
Merge pull request #1167 from mirage/mirage-releases

+shared-memory-ring.0.4.2
+travis-senv.1.0.0
travis-senv: add tags
Merge pull request #1170 from mirage/travis-senv

+travis-senv.1.0.0