New formula: cv (Coreutils Viewer)

Homebrew formula for [BestPig/cv](https://github.com/BestPig/cv), which is an OS X-compatible fork of [Xfennec/cv](https://github.com/Xfennec/cv). Since the @BestPig fork is missing tags for 0.4 and 0.4.1, the formula is head-only. It seems that eventually the fork is going to be merged into [Xfennec/cv](https://github.com/Xfennec/cv) but I dunno, the formula could probably be migrated to use that repo when that happens.

Ref Xfennec/cv#30.