rework compilation process

- minify (some) JS
- minify HTML output (markdown-it output, for example, isn't minified)
- switch stylus to SASS as stylus is not well maintained

Probably worth considering too:
- pre-gzip everything, reconfigure webserver to use that
- better parallelization

package.json

@@ -4,16 +4,18 @@
   "description": "Static site generation code for my website.",
   "main": "index.js",
   "dependencies": {
-    "dayjs": "^1.8.27",
+    "dayjs": "^1.8.28",
     "fs-extra": "^8.1.0",
     "gray-matter": "^4.0.2",
     "handlebars": "^4.7.6",
+    "html-minifier": "^4.0.0",
     "markdown-it": "^10.0.0",
     "mustache": "^4.0.1",
     "nanoid": "^2.1.11",
     "pug": "^2.0.4",
     "ramda": "^0.26.1",
-    "stylus": "^0.54.7"
+    "sass": "^1.26.8",
+    "terser": "^4.8.0"
   },
   "license": "MIT"
 }