Improves error definitions.
Removes -[CBLDatabase (ReactiveCouchbaseLite) rcl_doSync:].
Improves CBLDatabase (ReactiveCouchbaseLite) tests.
Adds -[CBLDatabase rcl_scheduler].
Rewrites +[CBLManager (ReactiveCouchbaseLite) rcl_sharedInstance].
Adds -[CBLManager (ReactiveCouchbaseLite) rcl_scheduler].
Improves -[CBLManager (ReactiveCouchbaseLite) rcl_isOnScheduler].
Work on thread safety.
More improvements to CBLManager (ReactiveCouchbaseLite).