Merge pull request #103 from bgamari/master

nrf: Call pin_change_init

This was overlooked in 3397b6b4520aeaa4ebfc52f92552662908accf6f.
Add pmtest
pmtest: Disable USB regulator
pmtest: Cleanup
pmtest: Modify to cycle through power modes
Port to pin_change infrastructure
pmtest: Test VLLSx modes
pmtest: Ensure low-power modes are enabled
reduce power more, add measurements
adc: Disable band-gap buffer after calibration