Switch to NAN as a dependency

This is a little risky, I'm not *entirely* sure it's safe to pull in nan as a dependency and then look for it in *binding.gyp* with a `node -pe ..` to find the install location. I messed with this a bit in [downer-rangedel](https://github.com/rvagg/node-downer-rangedel) but for other reasons related to npm/node-gyp that's not really a production-ready project.

NAN@0.3.0 isn't quite ready yet, this is for the WIP version, the final release should be done soon I think.

/cc @kkoopa