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 `glob` was outdated, and it's easier to just toss it than to upgrade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 It was super outdated.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.

scripts/_improve-rejection-crashing.js

@@ -0,0 +1,20 @@
+"use strict"
+
+process.on("unhandledRejection", (e) => {
+	process.exitCode = 1
+
+	if (!e.stdout || !e.stderr) throw e
+
+	console.error(e.stack)
+
+	if (e.stdout?.length) {
+		console.error(e.stdout.toString("utf-8"))
+	}
+
+	if (e.stderr?.length) {
+		console.error(e.stderr.toString("utf-8"))
+	}
+
+	// eslint-disable-next-line no-process-exit
+	process.exit()
+})