Reshaping repo

The repo is designed for use with an existing builds.sr.ht service.
Besides lacking that, I am more interested in a containerized workflow
powered by a Makefile. Package source code will live in `pkgsrc/`,
packages will be built into `pkg/`, and packaging keys will be
generated into `keys/`.

Alos trimmed the packages down to what I will build.

Split out core.sr.ht migrations in post-upgrade

Update todo.sr.ht.post-upgrade

Initial pass on todo.sr.ht package