(SERVER-204) Subcommands for 'ruby' and 'irb'

Working implementations for ruby and irb to go along with the gem
subcommand. Acceptance tests need to be written, as well as docs.
Hmm, it looks like adding `"--"` as an extra element at the end of this vector breaks things and prevents the `--config` arg from getting into TK:
```
ᐅ lein ruby --config ~/.puppet-server --version


Missing required argument '--config'!
```
```
ᐅ lein ruby --version --config ~/.puppet-server


Missing required argument '--config'!
```