This PR changes the way before_eventname/after_eventname events are called when using non-unique events.
Attention: This is a breaking change for events that assumed to wrap only single events to be wrapped.

Reason for this change is that the expected behavior for before/after events for a call such as event.event_to_call(...) is that they are called before/after that specific line once.

What this PR does:

• rewrite the call to hook before/after events just once before/after a list of non-unique events are called
• before events may transform args and kwargs just as for unique events
• after events may transform the list of results of the whore non-unique event list
• adaptions to the documentation to make this behavior clearer
• added also a note to the documentation in register_event about the default event names init, main and final.