Don't specify a default for pressure_advance. Don't specify values
that are already at their default. Add to printers.test test case.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Based on the configuration for the CR20-2018.
Added support for BLtouch, save z-homing and
automatic bed leveling.
Signed-off-by: Matthias Roggo <bskp@posteo.ch>