gettoken exercise

[matthew-white]

I don't think the gettoken exercise is especially effective. I'm not even convinced that gettoken is the best way to solve the problem. For gettoken, I think it's enough to introduce the concept and show the example we do; the exercise is too much.

However, I do think the macros module needs more than one exercise, so I'd add one for macro lists or one about passing information across do-files.