Extending the new rspec integration syntax

[djcp]

We're starting to use rspec's new(ish?) integration test syntax more and more at thoughtbot (details) and it'd be nice to be able to extend the scenario / feature syntax similarly to describe / it. Thoughts? I may be able to hack on this if there's interest.

[michaelklishin]

@djcp I am all for keeping up with RSpec's changes and new features