New build process

Packages can now be built with `make`. The targets are all based on the
files that are served in the official mirror.

Re-added two dependencies of todo.sr.ht that I has missed.

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.