Render markdown files in tree view

[Andy Green]

Hi -

Thanks to John and Lukasz on the tree view rendering patches.  I joined
the list just now to ask about it and saw the recent posts.

After screenscraping and updating a little John's patches against HEAD:
they seem to work OK for me.  That's no ding on Lukasz's patches, I
don't know enough about cgit internals to make an informed choice, I
just picked John's on the basis they had been around longer.

I basically had to append:

render.md=/usr/lib/cgit/filters/about-formatting.sh

to the config and I could see rendered .md in tree view.

So I wanted to relate my experience and gently encourage the maintainer
to include some implementation of this valuable feature.  It basically
allows nice generic documentation and "git based wiki" without any
special support over just having cgit anyway.  "Culturally" in-tree
markdown docs have become a thing thanks to github, this is a small
additional feature but it goes quite a long way with enabling that for
sites using cgit.

-Andy