chore: Significantly restructure folder layout

This moves the various projects from "type-based" folders (such as
"services" or "tools") into more appropriate semantic folders (such as
"nix", "ops" or "web").

Deprecated projects (nixcon-demo & gotest) which only existed for
testing/demonstration purposes have been removed.

(Note: *all* builds are broken with this commit)

fun/aoc2019/default.nix

@@ -0,0 +1,22 @@
+# Solutions for Advent of Code 2019, written in Emacs Lisp.
+#
+# For each day a new file is created as "solution-day$n.el".
+{ pkgs, ... }:
+
+let
+  inherit (builtins) attrNames filter head listToAttrs match readDir;
+  dir = readDir ./.;
+  matchSolution = match "solution-(.*)\.el";
+  isSolution = f: (matchSolution f) != null;
+  getDay = f: head (matchSolution f);
+
+  solutionFiles = filter (e: dir."${e}" == "regular" && isSolution e) (attrNames dir);
+  solutions = map (f: let day = getDay f; in {
+    name = day;
+    value = pkgs.writeElispBin {
+      name = "aoc2019";
+      deps = p: with p; [ dash s ht ];
+      src = ./. + ("/" + f);
+    };
+  }) solutionFiles;
+in listToAttrs solutions