Test against latest Ember RC2 and RC3 gems, and Rails 3.1, 3.2 and 4, and specify gem dependencies accordingly.

[Fixes #165 #168]
Merge pull request #179 from yappbox/dependencies-and-appraisals

Update ember-source dependency and appraisals
Removed maximum ember-source restriction, added note to README about specifying ember-source version in Gemfile, bumped tests to run against the new ember-source 1.0.0rc3.2 @lukemelia / @stefanpenner / @kagemusha
Merge pull request #180 from yappbox/version-fun

Make versioning approach a little more user-friendly
bump version