Fixes incorrect method name in down migration
Adds omitted opts hash key to down migration
Adds ::rollback method to Songkick::Oauth2::Schema

Also updates README to indicate the availability
of the rollback method.

(Also aliased as ::down)
Merge pull request #59 from gregates/down_migrations_revised

Bugfixes for down migrations, and a rollback method
FIX: Accept params in the POST body as JSON

When creating a token accept params passed as JSON in the POST body
Check for nil content_type
Merge remote-tracking branch 'upstream/master' into upstream-master
Mark mass-asign specs as pending
Merge branch 'parse-json-body' into upstream-master