Expand user name tests to include _ and -

[NicMcPhee]

There are user names with _ and - in the full data set, but none in the test data until you get to the final test. It might be good to have examples in the partial tests that include those so people get a heads up sooner.

[NicMcPhee]

I haven't really fixed this, but I did add a comment to the README about it so they have a heads up (if they read carefully, and remember).

[NicMcPhee]

Actually, I'm not sure I want to add these to the tests. We've warned them in the write-up that the tests don't cover these specific things, which is a lot more warning than people get in the Real World. I'm inclined to let this go for now.