This patch also removes the empty type "pinbase_type" (which crashes if
accessed) and uses "machine_pinbase_type" instead as the type of the
PinBase singleton.
Allows to translate C-level pin API to Python-level pin API. In other
words, allows to implement a pin class and Python which will be usable
for efficient C-coded algorithms, like bitbanging SPI/I2C, time_pulse,
etc.