add support for cyclic garbage collection to eTimer and eSocketNotifier

add support for cyclic garbage collection to eTimer and eSocketNotifier
class, add simpler method to set a timer callback.. or remove.. instead of
timer.timeout.get().append(func).. or .remove(func)... now it is possible to
do timer.callback.append(func)... timer.callback.remove(func) (the old
method still works..but is now deprecated)