Document pointed things

[appgurueu]

See https://dev.minetest.net/pointed_thing

[benrob0329]

I think that this is where using a visual aid would be helpful. The main plugin to make this easy is here, and I'm trying to see which option would best support our use-case here.

EDIT: I'm leaning towards Gnuplot, since it supports a variety of output formats (we could have text output for man pages, svg for everything else), and will be able to do whatever we want (and we can probably abuse macros to make writing quick plots easier since it supports functions).

Also, cubes: http://www.gnuplotting.org/plotting-cubes/