first refactoring of Instances:

* use long values to store the values of an instance. The new Instances class is merely a collection of static routines to do the math.
* use long arrays instead of a TreeSet to store the instances, that saves many object instantiations and time. Sine most instances are created in chronological order there is no reason to insert them sorted. The few mehtods that require it can call a sort method.
* introduce new classes CalendarMetrics and GregorianCalendarMetrics to provide better support for other calendar scales and to speed up calculations
* start to replace all calendar calculations using CalendarMetrics
* drop support for Iterable. It required an object to return and doesn't play well with long values

In most cases the new code is twice as fast as the old one. There is still some work to be done, this is just the first step. There is still much room for improvements.
Merge branch 'master' of ssh://git.dmfs.org:23023/libraries/lib-recur