Simple Extension implemented in Shimmie core

Simple Extension functionality was imported into Shimmie core earlier this week. If you have this extension active, PHP will complain that you can't define SimpleExtension twice.

There were some changes during the import due to some problems with the Shimmie forum (broke during upgrade to phpBB3) and Shish ended up re-implementing it in core rather than performing a true import.

Unlike my version, which merely forwarded execution to functions of the same name as the event, this implementation prepends "on" and removes the trailing "Event." So an event PageRequestEvent will call a function onPageRequest.

This method, however, removes the need for the acrobatics my version was performing to prevent the forwarding from calling the receive_event and new i_am functions. The event_method_callable function is thus not needed and was not used.

I have not yet updated the source of my extensions that used this, though Shish has already made most (if not all) of the core and core-maintained extensions use it.