Support different numbers of "quadrants" in technology radar

I was using this (excellent!) tool to create a technology radar for internal use.  I could only think of three appropriate quadrants, so this pull request improves the support for that by not drawing a 2x2 grid in the middle of the circle, instead drawing the appropriate number of lines outwards from the center of the arc.

I've probably explained that poorly, so here's a picture of a technology radar with three quadrants (quadrants is now poorly named, but I didn't want to make the commit noisy!).

![example](https://f.cloud.github.com/assets/15318/1171894/721c3570-2111-11e3-8be8-2767da48d40b.PNG)