- On pwm_poweron, the PWM resolution was not restored. (A custom resolution was
only usable if, PWM channel 0 is not used. That configuration is not common,
so this bug was likely never triggered)
- Disabled a work around to prevent flickering:
- Previously, PWM was disconnected on level 0% and 100%
- This increases the run time of `pwm_set()`
- It prevents using the PWM for wave form generation via DDS, as the wave
noticeably jumps when reaching 0% or 100%
- Slightly reduces memory requirements: 2 Bytes of RAM, 112 Bytes of ROM
- Tested with avr-gcc 9.2.0 and LTO enabled
