sleep functionality added - first attempt
Removed switchToHSXOSC() and used boardClockInit() instead. This fixes the problem where the flash cache wasn't being re-enabled after going into PM2 and PM3.

Also added in restoration of DMA descriptor after PM2 and PM3. Sleep timer resolution is also set just before entering sleep (instead of sleepInit) to assist with radio_mac compatibility.
Merge branch 'master' of http://github.com/pololu/wixel-sdk
Merge remote-tracking branch 'lummo/master'
Ignore .lk and .omf files
Move sleepInit() out of board.c. Apps should call it after systemInit() if they need sleep functionality
Some minor clean up of sleep related code
First pass at adding radio shutdown
Fix bug in radioMacResume(). Enable the RF interupt outisde the is statement
Added test_radio_sleep app
Merge remote-tracking branch 'slasi/radio'