#65 automatic update feature

[Eran]

It seems particulary essential in case that Yahoo site is
changed in a way that requires a critical fix in YPops.

For example, when I had version 0.7.0 beta, mail
deletion suddenly stopped working (due to a change in
Yahoo site). So the same emails were downloaded
multiple times. I fixed the problem by installing a later
version of YPops. It would be convenient if an automatic
update could do that for me, so I would not even notice a
problem existed at first place.