Rewrite docs linter

1. I want to set the stage to deal with #2898 properly.
2. `request` was deprecated years ago. Decided that it's better to just
   move to native Node.js APIs in its place.
3. `glob` was outdated, and it's easier to just toss it than to upgrade
   across a major version.
4. I switched to using Marked's "lexer" directly so I'm not fussing
   with the complexity of renderers. This of course necessitated a more
   complex file processor as its "lexer" is really an AST parser.

I also decided to go a few steps further:
- Drop the cache to simplify everything. I might reverse this later,
  but just caching URLs per-page should be enough to prevent the world
  from crashing down.
- Drop some more dependencies, so I don't have to come back to this
  later nearly as quickly.
- Upgrade to a more modern language version in the scripts.
- Update Marked. It was super outdated.
- Add line and column numbers to the warnings. That took quite a bit of
  work, thanks to a missing Marked feature plus a bug in Marked.

package.json

@@ -17,10 +17,10 @@
     "build:docs": "node scripts/generate-docs",
     "build:min": "node scripts/bundler browser.js -output mithril.min.js -minify -save",
     "build:stream-min": "node scripts/minify-stream",
-    "cleanup:lint": "rimraf .eslintcache .lint-docs-cache",
+    "cleanup:lint": "rimraf .eslintcache",
     "lint": "run-s -cn lint:**",
     "lint:js": "eslint . --cache",
-    "lint:docs": "node scripts/lint-docs --cache",
+    "lint:docs": "node scripts/lint-docs",
     "perf": "node performance/test-perf.js",
     "pretest": "npm run lint",
     "test": "run-s test:js",
@@ -40,13 +40,11 @@
     "istanbul": "^0.4.5",
     "lint-staged": "^13.2.1",
     "locater": "^1.3.0",
-    "marked": "^4.0.10",
+    "marked": "^14.1.0",
     "minimist": "^1.2.0",
     "npm-run-all": "^4.1.5",
     "ospec": "4.1.6",
     "pinpoint": "^1.1.0",
-    "request": "^2.88.0",
-    "request-promise-native": "^1.0.7",
     "rimraf": "^3.0.0",
     "semver": "^6.3.0",
     "terser": "^4.3.4"