tmp275: Fix one shot mode and update comments.
HAL: Add comments for GDOx modes.
led: Clarify comments.
adc: Rewrite to enable multichannel measurements.
rf: Use busyloop instead of actual sleep.

Use faster polling rate for the idle check. Also busyloop seems to
work more reliable.
utils: Add busysleep_us().
wireless-soil-solar: Add new project.
application: Update to use the new ADC API.