added links to index and constraints to rest api root
added index listing
added list of rest api surface endpoints
Unique constraint verification: Use document frequency

This is provided directly by lucene so we don't need to maintain an
external term counter.
Update another Javadoc on read ops in tx.
Depend on the correct Java version

The Oracle JVM has a different package name, which will be addressed
in a future commit.
Merge pull request #1804 from apcj/term-freq

Unique constraint verification: Use document frequency
Merge pull request #1749 from lassewesth/restapiindexlink

added links to index and constraints to rest api root
Merge pull request #1801 from jotomo/tx-all-over-the-place

Update another Javadoc on read ops in tx.
Fixing doc bugs.