treewide: manually convert some docs to Markdown

These files all have options that trip up the `nix-doc-munge`
conversion tool for one reason or another (syntax that clashes with
Markdown, options that were already using Markdown syntax despite not
being marked that way, output that differs slightly after conversion,
syntax too elaborate to convert with some cheap regular expressions,
...). Translate them manually and do a little copyediting to options
in the vicinity while we're at it.

modules/programs/vscode/haskell.nix

@@ -35,12 +35,15 @@ in {
       type = types.path;
       default = defaultHieNixExe;
       defaultText = defaultHieNixExeText;
-      description = ''
+      description = lib.mdDoc ''
         The path to the Haskell IDE Engine executable.
-        </para><para>
+
         Because hie-nix is not packaged in Nixpkgs, you need to add it as an
         overlay or set this option. Example overlay configuration:
-        <programlisting language="nix">${exampleOverlay}</programlisting>
+
+        ```nix
+        ${exampleOverlay}
+        ```
       '';
       example = literalExpression ''
         (import ~/src/haskell-ide-engine {}).hies + "/bin/hie-wrapper";