Some massive changes to make flakiness better

Renamed the @inputs to @top. This was a misguided attempt to make a
different change, but it's going to stick, now.
Began moving packages to their own folder rather than being intermingled
with overlays
Created a local overlay that just includes my personal packages
Cleaned up some dead code
Moved to just using the raw 'imports' instead of needing to explicitly
call out the `foo = import foo.nix {};` syntax

pkgs/default.nix

@@ -0,0 +1,13 @@
+{ pkgs, ... }:
+
+let
+  c = pkgs.callPackage;
+in
+{
+  packages = {
+    #default = iso;
+    #iso = top.self.nixosConfigurations.iso.config.system.build.isoImage;
+    #iso-beta = self.nixosConfigurations.iso-beta.config.system.build.isoImage;
+    hms = c ./hms { };
+  };
+}