Implementation of interrupt driven binary switch

The difference between the interrupt driven binary switch example and
the normal binary switch example is the following:
* Interrupt example does not use debouncer because it rely on loop()
iterating over time (but it sleeps between iterations)
* Interrupt example is more power conservative because it sleeps as soon
as it has sent updated data and no activity happens on the pin
* Interrupt example is limited to only two IO pins for the sensor, due
to limitations in the Arduino HW. The example uses the preprocessor to
ensure that this is not misconfigured or sleep function can not be
expected to behave as intended.
Merge pull request #30 from fallberg/development

Implementation of interrupt driven binary switch