use NAN for Node 0.8->0.11+ compatibility

Node 0.11 and onwards uses the new V8 which has huge breaking API changes. [NAN](https://github.com/rvagg/nan) is designed to make it easy to support V8 and Node across versions 0.8 to 0.11 and onwards without the need for branching macros. NAN is keeping up-to-date as newer versions of Node 0.11 are released and new breaking changes come upstream from V8.

This PR adds NAN support for compiling against the latest Node 0.11; tests pass.

Let me know if you have any questions, I'd love to get an 0.11 version of dtrace-provider into npm so we can start testing in preparation for the impending 0.12 release.