Benchmark and optimize output size

Test repo source code size during tests: 7.2 MiB

Full ToC removal with hack:

 function renderTocFromEntryList({ add_test_instrumentation, entry_list, descendant_count_html, tocIdPrefix }) {
+  return ''

Test repo output size: 166.6 MB -> 114.2 MB, so ToC was 31 %

Let's check header knockout with:

        [Macro.HEADER_MACRO_NAME]: function(ast, context, opts={}) {
          return ''

down to 151.7 MiB, so headers were about 9%.

And finally removing the toplevel stuff:

       toplevel_child_modifier: function(ast, context, out) {
+        return 'out'

down to 161.8 MB, so these were only about 3%.

These should be the only bulk things we have really, everything else will likely be much harder to get wrong.

 Ancestors