redding/rb — pull request #39 by kellyredding (2013-12-22 23:11:17+00:00)
Title: `rb each` command for running a command across all installed rubies

This command work much like `rb exec` except it runs the given cmd,
not against a _given_ rubie, but against _all installed_ rubies.

The particular use-case I have in mind for this cmd is for running
a build against multiple rubies.

Closes #38.

@jcredding ready for review.