Problem

Currently to disconnect a callback in a callback registry you need to keep track of the connection id. It'd be easier to use if you could instead just pass the function to disconnect.

Proposed solution

Allow for the following:

reg = CallbackRegistry()

def f1():
   pass

cid = reg.connect("something", f1)

reg.disconnect_func("something", f1) 
# above is equivalent to reg.disconnect(cid)