escape web concept values

[dret]

individual web concept values should be escaped in the web concept URIs. this would avoid problems with values that have slashes (such as media types) or hash signs (such as some profile URIs). while not so hard to do in principle, this causes problems with jekyll and github pages. jekyll/jekyll#6052 has been raised to address these problems, but this might take a while to fix because there seem to be various problems with jekyll itself, and with the web server and its ability to properly respond to requests for URIs containing escaped characters.