Updates to billing/README file.
Fix couchrest model migrations to work with latest version

Also we now depend upon couchrest model ~> 2.0.0. The beta2 still has the old naming scheme for CouchRest::Model::Utils::Migrate
Merge pull request #95 from azul/hotfix/4080-couchrest-model-breaks-bundle

Fix couchrest model migrations to work with latest version
Merge remote-tracking branch 'leap/develop'
Version 0.2.4
Merge pull request #96 from azul/release/0.2.4

Release/0.2.4
Merge branch 'develop' into feature/billing-past-due-subscriptions