PushButton and Pingo

[s-celles]

We might consider

pingo-io/pingo-py#98
pingo-io/pingo-py#107

and merge code from

https://github.com/RaspberryPi-Samples/io/blob/master/pingo_parts_pushbutton_long_short.py

to

https://github.com/pingo-io/pingo-py/blob/master/pingo/parts/button.py

(see also https://github.com/pingo-io/pingo-py/blob/master/pingo/parts/led.py )