nimrod-lang: New and improved formulas

This pull request attempts to improve Homebrew's support for the Nimrod language by supplying two new and improved formulas. The explanation for the changes are in the commits themselves, and I'd also be happy to answer any questions about this here.
I understand, but I think that this is an instance where simplicity is not always the best.

The old formula downloads a zip file supplied by upstream which contains bootstrap stages and uses the supplied build scripts which utilize the bootstrap stages. The problem with this is that a bootstrap stage is bound to an architecture and OS combination, so to get around this upstream provides many different bootstrap stages in the zip file. If you happen to have an arch-OS combination that is not supplied by upstream, then you're out of luck.

Upstream currently includes bootstrap stages for 32-bit and 64-bit OS X, and I'm not saying that this is going to change. But the choice here is whether we want Homebrew to be more robust or not, and I vote for more robust. Going the more robust route doesn't add much more complexity than the non-robust route, the majority of the install method is working around OS X-specific bugs in Nimrod, which will be needed regardless of which route we go here.