Added implementation of hardware PWM helpers.
Added systick implementation.
More work on the TIMER1 functions (system ticks and software PWM).
Changed ticks and software PWM to use a 64Hz cycle (with 64 subcycles for 'ticklets' and PWM adjustments). This uses a prescaler of 2048 (for an 8MHz clock) and means an interrupt every 2000 instructions or so. The ISR is about 100 instructions long which means we use up about 5% of the CPU capacity generating the output.
Updating implementation of systicks.
Merge branch 'master' of memoir.homeip.net:quickies/bluebell

Conflicts:
	firmware/shared/systicks.c
Fixed typo in #if statement for enabling output pin.
Fixed error in prescaler selection - now really divide by 8
Allow choosing a different serial port by using PORT=xxx when invoking
'make flash'
Fixed logic error in PWM generation, added function to query current
PWM level.