Added support for Dalli read_multi, reduce memcache call load.
Added a spec to make sure we don't call .fetch.
Workaround for Dalli frozen keys.
Updated history.
Minor: don't create many sets.
Removing the recursive materialization of JSON references.
Fix: null reference keeps track of its parent and can be removed.
Fix: as_json on hash/array without references.
Fix: mongoid_criteria.
Objects returned by Mongoid::Criteria aren't always including CachedJson.
Fix: return self from the key reference when there're no keys to merge.
Renamed variables to avoid confusion with Hash::keys.
Added notes on performance optimizations.
Updated links.
Moved HISTORY to CHANGELOG, updated README.
Fix: CHANGELOG entry not underlined.
Namespaced Mongoid::CachedJson::KeyReferences.
Moved some code around.
Merge pull request #9 from dblock/read-multi-ref

@macreery => Read multi ref