matrix-appservice-irc: init at 0.22.0

bird-lg: init at 2020-05-20-unstable

Merge branch 'macos-ci' into master

drep: Depend on CoreServices on macOS

Redefine package set on top of overlays

I wanted to reduce duplication, but ended up somewhat in the same place
(with manifest.nix).  Yet I find it much more elegant.

Rename overlay parameters to match flake style

iwgtk: init at 0.4

esbuild: init at 0.7.8

shellharden: init at 4.1.2

trust-dns: init at 0.19.5

guile-json: init at 4.3.0

drep: init at 0.1.1

starship: remove

It's been so long since I last used it that it's already been added to
Nixpkgs.

Fix python3Packages outside overlay, and other formatting issues

haunt: init at 0.2.4

guile-commonmark: init at 0.1.2

Split packages and modules off nixos-configurations

This will allow me to make them public while keeping the NixOS
configuration private.

Some reorganization was made to 1) be compatible with NUR, even though
I don't currently use it; and 2) mirror the nixpkgs taxonomy, to more
easily move packages upstream later on.

All package and NixOS module expressions were taken from
nixos-configurations@361ad13626117ee715ee1e215458329e8d0bada4.