This is a second go at #18472 with (in my opinion) a better approach using
subpackages instead of build time options.
libaldmb is a separate library that isn't used by the rest of the package
and splitting it avoids a bunch of unnecessary X11 & other desktop
dependencies on `dumb`.
For the reference player I created a `dumbplay` subpackage which keeps the SDL2
dependency out of the main library package, the tiny dumbout util has minimal
dependencies and thus probably belongs in the main package.
I also updated the homepage which still pointed to the old pre-fork page.
49243b3781