When printing the current workdir, use stderr instead of stdout.
This commit adds the functionality, in debug mode, for `revng daemon` to save when the SIGUSR2 signal is sent.
Package revng's python code in two wheels: `revng` and `revng_internal`. The revng wheel contains the `revng.{pipeline_description,model,tupletree}` modules, while the `revng_internal` one everything under `revng.internal`.