Improve compatibility with official active record API.

- change_column_null isn't officially supported (espacially in the jdbc h2 implementation)
- see http://api.rubyonrails.org/classes/ActiveRecord/Migration.html
Add support for testing the jdbch2 adapter.
Add Code Climate badge.
Merge pull request #109 from equinux/h2_support

H2 support
Use HTTPS for rubygems
Rapns.apns_feedback for one time feedback retrieval. Rapns.push no longer checks for feedback. Fixes #117, #105.
Update God config to allow for slow startup. Fixes #120.
Lazily connect to the APNs. Fixes #111.
Rescue Errno::EINVAL from IO.select. Fixes #119.
Adding 2.0.0 to CI.
Use cane with mri_20
Fix specs.
Get rid of shoulda.
Test master on Travis.
Ensure all notifications are sent when in push mode. Fixes #107.
Cleanup app runners when stopped. Fixes #106.
Only assign the connection if it connected.
Update changelog.
3.2.0
Mention apns_feedback in the readme [ci skip].