* Basic functionality for LRU eviction.
* Test eviction.
* Factor out eviction policy.
* Move delete_object into eviction policy.
* Replace array of released objects with an LRU cache (hash table + doubly linked list).
* Finish rebase on master.
* Move actual object deletion away from eviction policy and into plasma store.
* Small fixes.
* Fixes.
* Make remove_object_from_lru_cache always remove the object.
* Minor formatting and comments.
* Pass in allowed memory as argument to Plasma store.
* Small fix.
* Merge sealed_objects and open_objects into a single hashmap
* Entry contains enum that determines whether it is open or closed
* Removed unused variable.
* Applied Robert's patch
* Fixed styling.
