Feature/v0.11 support

node 0.12 is coming (really!) and we are updating our dependencies to get ready.

This PR removes some unused code that made compatibility with v0.11 harder, and then uses the compatibilty shim from bnoordhuis/node-heapdump to port to v0.11.

I think its a good idea, maybe ThrowException can be overloaded on` Local<String>` and `const char*`?