This PR moves dispatch_after and dispatch_group_async to class methods, so a subclass of FBLPromise could override the dispatch behavior (with access to FBLPromisePrivate.h).
Also updates a few other places to:
Use [self alloc] or [[self class] alloc] instead of [FBLPromise alloc], to make sure methods are allocating the same class as the instance (or class)
Use [FBLPromise class] in isKindOfClass: still, to not force exact subclass matching
This PR moves dispatch_after and dispatch_group_async to class methods, so a subclass of FBLPromise could override the dispatch behavior (with access to FBLPromisePrivate.h).
Also updates a few other places to: