Remove unmatched uv_unref() causing segfault

Also, properly close the async watcher when closing the port.

Fixes https://github.com/justinlatimer/node-midi/issues/16
Add installation prerequisites to README.

Document the dependency, as opposed to the non-idiomatic but well intentioned auto-install from #31
Update maintainers / contributors

* Add new maintainer @drewish - welcome!
* Add links to profiles for all contributors.
Tidy up formatting in the usage section.
Change format on stream files in examples

Should clear up confusion caused by using the .mid extension in #30.
Merge pull request #32 from drewish/node-0.10

Remove unmatched uv_unref() causing segfault
node-midi v0.7.1