I can't figure how to, by default, exclude everything and only include what I'm interested in.

If I've understood you correctly, I think it does in fact work the way you want it to. Have you tried including the files you are working on and leaving out the exclude?

eg:

include = 'src,test'

would only include the src and test directories without the need to exclude anything. You could then exclude anything you didn't want within those directions with your exclude.

Cheers,
George