Emits a signal.
Signal emission is done synchronously. The method will only return control after all handlers are called or signal emission was stopped.
Note that emit_by_name resets the return value to the default if no handlers are connected, in contrast to
the instance the signal is being emitted on.
a string of the form "signal-name:
parameters to be passed to the signal, followed by a location for the return value. If the return type of the signal is g_type_none, the return value location can be omitted. The number of parameters to pass to this function is defined when creating the signal.