Dependency logic

[qazwsxal]

Need to figure out the logic to be used for dependency resolution.
https://fsprojects.github.io/Paket/resolver.html paket's dependency resolution algorithm
https://www.debian.org/doc/manuals/aptitude/ch02s03s02.en.html apt's algorithm

http://www.cas.mcmaster.ca/~cas724/2007/paper2.pdf lot of theory stuff here.

Cargo's dependency resolution algorithm doesn't seem applicable here, cargo "features" don't map to fsnebula "packages" well.

In apt terms, it's probably best to treat a "mod" as a meta-package made up of several packages, (some optional). Dependencies on FSN/knossos can be thought as "package depends on set of other packages". That way we can flatten the mod/package tree, just need to make sure that a selected group of packages from the same mod have the same semver.