Merge pull request #69 from die-antwort/make-compatible-with-rspec3

Adapt TextMateFormatter for RSpec 3, use RSpec’s own TextMateFormatter for RSpec 1 & 2
Use rspec binstub if available.

Look for "bin/rspec" and use it, if present. This drastically improves RSpec’s start up time for projects using an application preloader like Spring (as long as the preloader generates a suitable binstub).