Modified Pimorini Fanshim Code for slower Quieter running using PWM

Cloned the official code and made minimal changes so it runs at 80% speed instead of 100%. 

Especiallly with the Pi making less heat due to recent firmware changes this lower speed is more than sufficient and is far quieter.   For example at at 1100% Load Test for 15 minutes using the 80% speed the CPU temperature settled at 59C.

See the Readme files at  Github.com/grayerbeard/fanshim-python and https://github.com/DT-was-an-ET/fanshim-python-pwm  and also  github.com/pimoroni/fanshim-python/issues/22

In February 2020 checked out the changes on an R Pi 4 running Volumio (a specialized Media Player OS from volumio.org/get-started ) and added the necessary extra notes to get Python3 working on that minimal Jessie based system.