python: added pyA20 for controlling GPIO

pyA20 allows controlling GPIO, SPI and I2C on Allwinner boards.
Although it is named A20 it should work on A10, A13 and other CPUs.
Provided by Olimex for their boards but should work for other as well.
Tested on A20-OLinuXino-MICRO.

Signed-off-by: Jens Lucius <info@jenslucius.com>