added the new go_subscriptions_signup filter
call GoSubscriptions('subscription') and GoSubscriptions('billing') always since we were effectively doing this by firing the "goPostSignUp" event on every page already
implemented the go_subscriptions_signup_form filter to conditionally generate the step 2 CC form during user signup
Merge pull request #12 from wluo/freebird

Freebird: implemented sign-up form post redirect and generation as filters