Update for Nimrod -> Nim transition

As far as I can tell, the API changes in 0.10.0 shouldn't break of the internals (or at least, it hasn't in my own use of nake with the dev versions of Nim), but all of the invocations of the `nimrod` compiler need to be switched to `nim`, which this should do.  I've also gone and changed most of the documentation that I could see, including the codeblock names.

I haven't put together a proper release because a) effort, and b) this version shouldn't be merged into stable until 0.10.0 finally comes out.