Remove unnecessary codes in getAllTask
Add test for nestedTransaction
Modify nestedTransaction test to prevent false positive
Add mergedOperationsQueue and mergeQueue to ensure correctness of file being modified
Fixed taskID saving on exit.
Fixed lint.
Removed debug code.
Fix logic error on generating Task IDs
Fix bug in descending
Add unit test for comparators
Do not sort if no comparator given
Overload operator==
Implement mergeQueue
Minor modification to doc, add committedTransaction stack
Implement onTransactionCommit correctly (hopefully)
Modify test to get the singleton instead of instantiating every test
Add friend class DataStoreApiTest for cleaning up
Clean up after every test that uses Internal::DataStore
Rename mergeQueue to mergeOperationsQueue
Refactor execution of transaction out from onTransactionCommit