HTML in glossary items

[ajparsons]

With markdown transition, some old entries with HTML are now displaying like this:

Either needs a one-off automatic fix, or to be happy with HTML as well as markdown.

[struan]

I've set parsedown to not escape HTML for now which will be fine as it's all checked anyway. Long term we probably want to run it through something like http://htmlpurifier.org/ just to be sure.