Add tests
Ported to NAN, compiles on v0.11.14

I have ported the module to NAN, effectively allowing build on node
v0.11. I have confirmed the module still works on v0.10.29 and all
tests are passing.
Merge remote-tracking branch 'origin/tests'
Merge remote-tracking branch 'origin/nan'
Async callback return null on success (fixes #5)