Sleep mode enabled

Sleepmode  is power_save. Timer2 wakes at 9.85mS. On interrupt tick is
incremented. When 100 ticks have been processed approx. 1 second has
elapsed. The ticks drive an "RTC" to get minutes and hours. Every minute
a reading is taken from the MPL3115 and stored in the SD card.

Power savings have not been tested at this point. I need a better µamp
meter.