Include the /docs folder on docs.wikimedia.org

• Includes .md files in Doxygens input
• Converts all /docs docs from wiki to .md so that Doxygen can render them. The idea would be that we stop copying these to mw.org and instead link to the generated docs.
• Create a page collecting all ADRs
• Create a page collection all other "topics"
• Use the main README.md file as the main page for the generated docs
• Excludes some submodules from the docs input so that Doxygen doesnt pick up the extra markdown files

Some things to think about, but that shouldnt block the merging of this:

• Should the JS hooks docs live here?
• TODO add more links between the docs and the code
• TODO cleanup the XXXX ADR
• Shoud the ADR template render in the docs?
• TODO clean up and update docs...

Change-Id: Ifb6d3b5ef050c1cfbd2b035a58f63c976721b1cb