Updates for Rails 4 and Ruby 2.0

Thanks for the tips from @daniel-rikowski on issue #59, I managed to make `delocalize` work on Rails 4 RC1.

Some tests are still not passing, though… I found 3 issues:

* Timecop does not seem to work very well on Ruby 2.0, so some tests that rely on it are failing;
* Looks like Rails 4 does not emit the "size" attribute on input tags anymore, so I had to remove those from the ActionView tests in order to make them pass;
* Some decimals are being translated to `BigDecimal` instances, which are not comparable.

Other than that, this changes should be working just fine.