treewide: convert options with tables to Markdown

The Markdown options processor cannot handle rendering tables
to DocBook.  This could be fixed, but as we won't be using the
DocBook output for long I just removed them for now in the interest
of expediency; they were all well-suited to being description lists
showing option types anyway, apart from one awkward case in the form
of trayer, which also had ad-hoc syntax for enumerating acceptable
values in the documentation. Since the types aren't actually used for
option processing anyway, I changed them to use `enum` and similar to
give a single description of the acceptable values without a big table.

modules/programs/vim.nix

@@ -89,23 +89,19 @@ in {
             background = "dark";
           }
         '';
-        description = ''
+        description = lib.mdDoc ''
           At attribute set of Vim settings. The attribute names and
           corresponding values must be among the following supported
           options.
 
-          <informaltable frame="none"><tgroup cols="1"><tbody>
           ${concatStringsSep "\n" (mapAttrsToList (n: v: ''
-            <row>
-              <entry><varname>${n}</varname></entry>
-              <entry>${v.description}</entry>
-            </row>
+            {var}`${n}`
+            : ${v.description}
           '') knownSettings)}
-          </tbody></tgroup></informaltable>
 
           See the Vim documentation for detailed descriptions of these
-          options. Note, use <varname>extraConfig</varname> to
-          manually set any options not listed above.
+          options. Use [](#opt-programs.vim.extraConfig) to manually
+          set any options not listed above.
         '';
       };