opStrategy and ordering for ArithmeticPostAgg

Fixes #510
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
fix some rt cleanup and failure edge cases
address cr
Updates Cassandra example documentation.

Updates the required properties to enable Cassandra as deep storage.
Also adds more information about how to create the required keystore,
and which properties files need to be modified to support Cassandra.
Also adds syntax highlighting to the provided example code.

Additionally, moves Cassandra Deep Storage documentation out into the
actual documentation hierarchy with appropriate linkage. A stub
README.md is left in the example directory to provide a useful landing
page for existing weblinks to the original documentation.
address cr
add more logging
Merge pull request #681 from metamx/fix-rt

fix some rt cleanup and failure edge cases
Merge pull request #680 from lexicalunit/update-cassandra-example

Updates Cassandra example documentation.
prepare for next release
[maven-release-plugin] prepare release druid-0.6.145