feat: flatten namespaces on index pages

[kitsonk]

Ref #3

This is part 1 of what I suggested in #3, where namespaces are flattened on the index page, so "all" symbols are listed.

Here is what it looks like for /deno/stable now:

And here is what it looks like for oak:

[lucacasonato]

Thanks, this really helps with navigability.

Also kudos to how easy it is to do local development! Just checked out the repo and executed ./main.ts and everything just works. Very nice :-)

[bartlomieju]

LGTM too, great improvement

[kitsonk]

Ok, I will write up some tests then this morning.