Remove runtime dependency on RSpec

It's actually quite problematic.  It forbids from using prerelease
RSpec 3.  It forbids adding other test framework integrations (if anyone
wants to do it someday).  Many gems which provide matchers
(Shoulda Expectations, Capybara) skip this dependency.

RSpec is now a development dependency specified in Gemfile.
temp
Add RSpec 3 support
trigger travis