Splice ./universe directory into ./

Manually merging:
- README.md: I added the description from universe/README.md into the heading of
  dotfiles/README.md.
- .envrc: dotfiles/.envrc was a superset of universe/.envrc
- .gitignore: Adding some of the ignored patterns from universe/.gitignore to
  dotfiles/.gitignore

Everything else here should be a simple rename.

default.nix

@@ -0,0 +1,37 @@
+# At the time of this writing, this configuration was taken from @tazjin's
+# default.nix from his depot. I've added, changed, and removed that parts that I
+# don't need, and this is what remains.
+{ ... }@args:
+
+with builtins;
+
+let
+  fix = f: let x = f x; in x;
+
+  # Global configuration that all packages are called with.
+  config = pkgs: {
+    inherit pkgs;
+  };
+
+  readTree' = import ~/depot/nix/readTree {};
+
+  # TODO: Find a better way to expose entire monorepo without introducing
+  # "infinite recursion".
+  localPkgs = readTree: {
+    blog = readTree ./blog;
+    lisp = readTree ./lisp;
+    third_party = readTree ./third_party;
+  };
+in fix(self: {
+  config = config self;
+
+  # Expose readTree for downstream repo consumers.
+  readTree = {
+    __functor = x: (readTree' x.config);
+    config = self.config;
+  };
+}
+
+# Add local packages as structured by readTree
+// (localPkgs (readTree' (self.config // { inherit (self) lib; })))
+)