watchdog: reworked to add support for software reset.

support for software reset due to watchdog timeout...
	based on watchdog documentation.

	modified:   sim/sim_avr.c
		modifications to avr_reset and avr_init to support software
			reset.

	modified:   sim/sim_avr.h
		added type avr_run_t...
		avr_t.run updated accordingly.

	modified:   sim/avr_watchdog.c
		largely rewritten to support software reset.

	modified:   sim/avr_watchdog.h
		data record 'reset_context' added to support software reset

	modified:   sim/sim_regbit.h
		added: avr_regbit_from_value
			for checking flags before commiting register value.
		added: avr_regbit_set_array_from_value
			reverse operation of avr_regbit_get_array