#47 get rid of containsKeys()
 #47 change API to use Map.Entry instead of Cache.Entry
 #47 trivial implementation of bulk ops
 #47 implementation of bulk ops with readers/writers + basic tests
 #47 better test coverage + bug fixes
 #47 add javadoc for Store's bulk compute methods
Merge pull request #105 from lorban/issue-47

Merged #105.