Add support for complex postaggregations

Postaggregations involving more than a single operator can now be built
Add Squeel acknowledgement to readme
update README
add js filters for gt, lt operators
dry the filters a little
add js filter flexibility
merge with master
fix js filter for string comparison
update readme for js filtering
split query code into separate files
add having clause to query
Updated README and gemspec
fix link in README
zookeeper could return invalid uri
Reverted code change to have a fallback instead of an implementation change
Fix merge