Improve callback calling to be sent to the Frame and executed when message is received by App (couldn't explain it in a simpler way :P )
Callback method and the event that should be published when message is received are now sent ONLY by the invoking method.
- Introduce @method subscribe_once that takes care of unsubscribing after the event has been triggered
- Fixes and issue with unsubscribing (wasn't really working before this commit)
Add .gitignore file