Labeledtree 201405a1

LUCENE-5627

This closes #46

Major overhaul:
- Renamed ...StreamsFactory to ...Analyzer to conform to lucene naming.
- Reasonably complete javadocs and tests.
- Added a tree for the labels.
- Added an analyzer for xml: tags as labels, attributes and text as fragments.

Based on recent efbytesref, LUCENE-5524, which is based on recent trunk.