Create .travis.yml

initial contents
Update mock_em.gemspec

added rake dev dependency
added Rakefile for running rspecs. removed old ruby-debug
added badges for travis-ci, gemnasium, badge.fury.io.  upgraded timecop
reduced timecop version to one compatible with Ruby 1.8.7
Merge pull request #1 from slatteryjim/master

added Travis CI testing for various Ruby versions