Course content, now CC-BY-NC

I added a notice to my previous courses notes to indicate that they are now available under the CC-BY-NC license. I don't know if it'll be in any way useful -- as I'm well aware the courses could use a huge amount of improvement (working on it!) -- but it seems worth doing.

Note to interested parties: If you're only looking for exercises to use in your own courses, don't worry about the license and just grab them. I would only humbly request, that you feel very free to also share back any exercise or resources you found useful to teach the basics -- I always struggle to find more! :-) Add a comment or contact me directly.