* Add priority queue to sdk
* fix issue of storing pointers and now copy
* update to use copy structure
* Remove file, put Item struct def. into other file
* add link
* clean up docs
* refactor internal data structure to hide heap method implementations. Other cleanup after feedback
* rename PushItem and PopItem to just Push/Pop, after encapsulating the heap methods
* updates after feedback
* refactoring/renaming
* guard against pushing a nil item
* minor updates after feedback
* Add read lock to the Len() method and move the interface check into the test file
* fix a deadlock
* make the mutex a RWMutex, and make it private again
* nil check itemRaw before trying to type cast it
