New RRULE parser.

This one is more lean as I've stripped out all the stuff related to
exceptions and overriding events.

This will allow me to refactor RecurrenceIterator to use RRuleParser and
fix all outstanding recurrenceiterator more elegantly.
Whitespace error.
Ripping the heart out of the old recurrence iterator.

very much a wip.
Lots more passing tests.
Fixed another bug.
fastForward takes the end time into consideration.
More passing tests.
Freebusy-related tests work again. Lots of other tiny bugs.
Multiple overridden events now behave correctly.
This unittest no longer makes sense.
Comments fixes. thnx @dominikTo
The first event can now be overwritten.

Fixes #18, #75, #58.
PHP 5.3
Merge pull request #106 from fruux/new-rrule-parser

New rrule parser