reduce object count overhead of column cache
add approximate object overhead
formatting
disable column cache by default
add column cache docs
add more logging for groupby caching
Merge pull request #675 from metamx/slimmer-column-cache

reduce object count overhead of column cache
prepare for next release
[maven-release-plugin] prepare release druid-0.6.144
[maven-release-plugin] prepare for next development iteration
Merge branch 'master' into druid-0.7.x

Conflicts:
	cassandra-storage/pom.xml
	common/pom.xml
	examples/config/historical/runtime.properties
	examples/config/overlord/runtime.properties
	examples/config/realtime/runtime.properties
	examples/pom.xml
	hdfs-storage/pom.xml
	histogram/pom.xml
	indexing-hadoop/pom.xml
	indexing-service/pom.xml
	kafka-eight/pom.xml
	kafka-seven/pom.xml
	pom.xml
	processing/pom.xml
	rabbitmq/pom.xml
	s3-extensions/pom.xml
	server/pom.xml
	services/pom.xml
fix compilation with Java 8