Add UNLOGGED, COUNTER options to BATCH docs

patch by Tyler Hobbs; reviewed by Sylvain Lebresne for CASSANDRA-6816
Add uuid() function
patch by Carl Yeksigian; reviewed by jbellis for CASSANDRA-6473
merge from 2.0
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	CHANGES.txt
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt