Add possibility sleep with watchdog disabled

[netmaniac]

Now, when we have pin change interrupt accessible maybe it is usable to provide deepSleep mode - with disabled watchdog. Pin change interrupt (and reset obviously) will wake tinyBrd up. Difference is that ATtiny @3.3V with watchdog enabled uses ~3.8 µA, and with WD disabled it will be even as low as 0.1 µA.