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
Remove `Ember::VERSION`

It should be defined in `ember-source`.
Merge pull request #182 from tricknotes/remove-ember-version

Remove `Ember::VERSION`
Register sprockets engine in config.before_initialize.
This fixes template compilation on Rails 4.0.0.rc1.
added ember data warning message to readme
Merge pull request #187 from kagemusha/ember-data-warning

added ember data warning message to readme
Update README.md
remove RC version requirements.

please specify the correct version of ember-source and handlebar-source
in your gemfile.

eg.

```ruby
gem 'ember-rails'
gem 'ember-source', '1.0.0rc3.3'
gem 'handlebars-source', '1.0.0rc4'
```
update readme
correct readme indentation
fix ember-source and handlebars-sources versions
fix failing tests, and remove gem files, no longer 
reference in the Appraisals file
add ruby 2.0.0 tests (and make them work)
Remove description about latest version

The version described in README.md is too hard to keep maintenance.
Merge pull request #194 from tricknotes/remove-version

Remove description about latest version
update readme, for latest version dependencies.

Once we are out of rc's we can stop with this madness.