allow a bundler-like way of specifying versions for Git Repos

This mimics (sort of) the bundler way of doing things:

    asset 'foo', '1.2.3', git: 'git@github.com:initech/foo'
    # same as
    asset 'foo', 'git@github.com:initech/foo#1.2.3'
add vim and rvm to ignores
Merge pull request #70 from stitchfix/feature/improve-dsl-for-git-repos

Enhance DSL for git repos