Revision 1645382

LUCENE-5648: spatial NumberRangePrefixTree refactorings, mostly:
* rename NRPT.LevelledValue -> UnitNRShape, NRPT.NRShape -> SpanUnitsNRShape, both subclass new NRPT.NRShape marker class; make all 3 public and use these types in method signatures as appropriate.
* remove NRPT pass-through convenience methods on NRPTStrategy (not needed; maintenance burden)
* re-order some factory/parsing methods in NRPT to keep together at the top
* UnitNRShape implements Comparable, and both NRShape implements Cloneable
* improve randomized test to pick better random calendars
* more docs