Class to make parallel bus out of arbitrary GPIOs.
Add example for ParBus, 2-LED "binary clock" ;-).
ParBus: Add enable(), input(), output() methods.
Rename "base" to "rest" to show recursive list processing nature better.
ParBus: Remove type_width param, limit bus to 8 bits.

If wider bus required, can eb easily made from few ParBus'es.
Give a hint that more targets supported.
Add initial class for HD44780 LCD devices.