edits to help file jsxgraph

[nick-chura]

I noticed that setting the 'face' of points, gliders and intersections won't accept camelCase, as in the help file, but rather only all lowercase. I edited the help file in those places.

[drlippman]

That's interesting. The JSXgraph documentation says it should be camelcase, but the code itself indeed expects lowercase. Weird.