+ Per Dmitriy, change the clone URL to github even though
  we'll continue using Kitware for MRs.
+ Add the remaining content from the old sensei-insitu.org site.
+ Per Seb, do not include full paths in `tpl/__sidebar__` so that
  highlighting of the current page works.
+ Change `doc/config.js` so that gh-pages is rooted at `/` instead
  of `/sensei` so that our custom domain works properly.
  Without this, the CSS file (at a minimum) is put in the wrong
  place.
+ Update the version of kw-doc we require to catch fixes from Seb.
+ Other small fixes.