Merge all script thingies at the package toplevel

Using subcommands at the top of the package is simpler and easier than
using individual script submodules.

Merger is mostly direct and ad-hoc, there was a minor amount of
deduplication (imports and the `file` argument, via parent parsers)
but that's about it so there may be opportunities for reducing the
size of the runner if someone bothers looking into it.

Author: masklinn