Add opts param to session#authroize_url to enable CSRF protection.
Use different method instead of opts for state param.
Use optional state param.
Cleanup session spec.
Merge branch 'state-param' of github.com:skalb/ruby-box into state-param
minor edits to spec.
Merge pull request #87 from attachmentsme/state-param

Add authorize_url_with_state to allow for CSRF protection.