Switch to npins & abandon haskell.nix

Flakes copy the whole gigantic repo to store all the time, quickly eating all the drive capacity.
haskell.nix is PITA to use on lower-spec devices.

npins/sources.json

@@ -0,0 +1,29 @@
+{
+  "pins": {
+    "hakyll-contrib-tojnar": {
+      "type": "Git",
+      "repository": {
+        "type": "GitLab",
+        "repo_path": "tojnar.cz/hakyll-contrib-tojnar",
+        "server": "https://gitlab.com/"
+      },
+      "branch": "master",
+      "revision": "v0.2.2",
+      "url": "https://gitlab.com/api/v4/projects/tojnar.cz%2Fhakyll-contrib-tojnar/repository/archive.tar.gz?sha=v0.2.2",
+      "hash": "1s9qjwadl0krzvs77d537pbyvr4mkkmjgdl79kc8lgil4y182v3m"
+    },
+    "nixpkgs": {
+      "type": "Git",
+      "repository": {
+        "type": "GitHub",
+        "owner": "NixOS",
+        "repo": "nixpkgs"
+      },
+      "branch": "nixpkgs-unstable",
+      "revision": "aeb75dba965e790de427b73315d5addf91a54955",
+      "url": "https://github.com/NixOS/nixpkgs/archive/aeb75dba965e790de427b73315d5addf91a54955.tar.gz",
+      "hash": "119lcwpkr9yy49z9fgpq32hp33igc4apbip2y2ppc7hwxs0hwyjk"
+    }
+  },
+  "version": 3
+}