Revert "Revert "Fix bug in loop run""

This reverts commit 4f9cc0e0ba220bc15287326ee9f173d03ccbc953.
Use unsafe module in tcp_sink
Update .travis.yml
Write more info in test.
Change. stat callback signature to `cb(loop, err, stat, path)`
Change. sync fs_XXX function returns true on success if there was cb.
Add. fs test.
Merge branch 'master' of https://github.com/moteus/lua-lluv