Homebrew (Alt-) Tap

This makes the tangram repository also function as a homebrew tap compatible with @telemachus's [brew any-tap](https://github.com/telemachus/homebrew-anytap)

This homebrew external command alternative to `brew tap` can be installed like so:
`brew tap telemachus/anytap`
`brew install brew-any-tap`

Then tap this repo with `brew any-tap`:
`brew any-tap tangram https://github.com/silentbicycle/tangram.git`

And install tangram:
`brew install tangram`

Resolves silentbicycle/tangram#1.