Add more values to exception hash in webhook call method
Add :data to exception hash in webhook call method
Add support for background notifications in webhook call method
Clean up body of sent exception in webhook notifier
Add License file
Add hipchat entry to Changelog.
Merge pull request #174 from buttercloud/extra_webhook_data

Added more values to exception hash in webhook call method
load attribute_accessors for ActiveSupport 4

When using ActiveSupport 4, we must explicitly load attribute_accessors
in order to use the mattr_accessor function in ExceptionNotifier.

Tested with ActiveSupport 4.0.0.

(Note that we only hit this bug when using ExceptionNotifier outside of
Bundler, since Gemfile.lock is presently locking activesupport to 3.2. I
assume that activesupport in exception_notification's Gemfile.lock will
be updated at some point in the future, at which point this will become
relevant to Bundler users as well.)