\return true if the queue is empty

Check whether list of connected slots is empty

* empty() method returns true if signal has any slots attached */

Determine if the signal is empty, i.e. no slots are connected to it. @returns `true` is returned if the signal has no connected slots, and `false` o

Expand memory by allocating new memory block May throw exception if memory allocation fails

Expand memory by allocating new memory block May throw exception if memory allocation fails

Fix pointers of removed elements to point after this element. Must be called under write_access() protection.