Adds create method to AuthCodeInterface. Relates to #160.
Merge pull request #176 from mdwheele/adds-authcode-create-method

Adds create method to AuthCodeInterface
Merge branch 'v4.0.0-WIP' of github.com:php-loep/oauth2-server into v4.0.0-WIP
Merge branch 'refs/heads/v4.0.0-WIP' into v4.0.0-relational-example