Convert scan code reference to markdown.

--HG--
branch : to-markdown
extra : rebase_source : 55553ecd106e86cce498e13d0f8b6ec0e3d0d0cb
Convert keycodes reference to Markdown.

--HG--
branch : to-markdown
Remove a stray (old) copy of welcome.html in img/
Merge Markdown conversion for keycode references.