More v0.2...

- Using interrupts for sensor readings (timer0 and 2, timer1 already in
use for PWM timing)
--- This requires a fix to wiring.c - the
MICROSECONDS_PER_TIMER0_OVERFLOW define must be updated to
(clockCyclesToMicroseconds(64 * 250)) due to new prescalar and overflow
counter
- updated battery monitor and load cell libraries to support this.