this is server side, and a more standard format, and thus I like it more
than mermaid, which I've been using at work. but, I really wanted a
server-side option (see my manifesto) for drawing relationship graphs,
for D&D stuff of all things.
this adds an optional 'graphviz' feature to package installation which
consequently depends on pydot
this has a really basic template and whatnot at the moment, so
styling/etc isn't done, but this is maybe the last major piece before I
could actually see pushing this onto the site
