Refactoring DHT11/22 device driver; replaced with interrupt driven variant.
Removing Event::Handler from ExternalInterrupt. Reduce multiple inheritance.
Ripple effect of removing Event::Handler from ExternalInterrupt.
Ripple effect of removing Event::Handler from ExternalInterrupt.
Refactoring PinChangeInterrupt; removing Event::Handler and changing to IOPin.
Ripple effect of replacing DHT11.hh and DHT22.hh with a single file DHT.hh.