use {{site.baseurl}} to enable future publishing on different paths

[JustBerkhout]

J: we use {{site.baseurl}}/assets/images/ for image references in markdown, but I think ../assets/images/ also works. Should we stick with {{site-baseurl}} A: yeah its so we can support hosting the site on other paths J: ok, so the handful of ../assets/ occurrences should really be fixed to {{site-baseurl}} then. A: I think so