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.
Best way is to override `ENV["HOME"]` or whatever other variables indicate where the packages are put so that they install into the temporary directory created by `test do` (and destroyed afterwards).