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.

`Return()` doesn't have a matching overload for int, and since js numbers are all doubles anyhow, double was the closest match.

I'll switch it to the new(to me)-style cast.