Prefetch occurrences in default get_events()

Suggest adding prefetch_related() to avoid N+1 queries. On my code queries per request went from 3000 to 20. It seems most anything you do with an event involves also looking at all the occurrences of that event, so this might be a more sensible default.
Add rule to prefetch

I guess the same logic applies for rule as well.
Merge pull request #78 from derek73/patch-1

Prefetch occurrences in default get_events()