A simple function pointer to get invoked when the signal is emitted.
This allows you to tie a hook to the signal type, so that it will trap all emissions of that signal, from any object.
You may not attach these to signals created with the NO_HOOKS flag.
Signal invocation hint, see SignalInvocationHint.
the instance on which the signal was emitted, followed by the parameters of the emission.
user data associated with the hook.
the number of parameters to the function, including the instance on which the signal was emitted.
whether it wants to stay connected. If it returns false, the signal hook is disconnected (and destroyed).