IRQ callback

[Premik]

The callback implemeted also the IRQ stuff.

• There are helper methods created in the irq module. Which is accessible on the main avr object.
• Currently helpers are only created for digital IO and ADC. But all the required IRQ methods/macros I found are already exposed on the swig level in the utils.i.
  For example to register a callback on pin change:

avr.irq.ioport_register_notify(myCallable, ("A", 6))

More comperhensive usage is in the test_irq.py.

This enables both-way communication between Python and simavr core. No need to create custom parts in C anymore just to be able to watch pin change etc.

[coveralls]

Coverage increased (+3.7%) to 82.261% when pulling a3f031b on Premik:IRQCallback into a04237d on ponty:master.

[coveralls]

Coverage increased (+3.7%) to 82.31% when pulling 2fb7d8a on Premik:IRQCallback into a04237d on ponty:master.

[coveralls]

Coverage increased (+3.7%) to 82.31% when pulling 2fb7d8a on Premik:IRQCallback into a04237d on ponty:master.

[coveralls]

Coverage increased (+3.7%) to 82.31% when pulling 2fb7d8a on Premik:IRQCallback into a04237d on ponty:master.

[coveralls]

Coverage increased (+3.7%) to 82.31% when pulling a2cc8f6 on Premik:IRQCallback into a04237d on ponty:master.

[coveralls]

Coverage increased (+3.7%) to 82.31% when pulling a2cc8f6 on Premik:IRQCallback into a04237d on ponty:master.

[coveralls]

Coverage increased (+3.7%) to 82.31% when pulling a2cc8f6 on Premik:IRQCallback into a04237d on ponty:master.