WIP: A rough version of the shell lessons based on Nelle

As discussed in #405 I recently taught a version of the novice shell lectures that focuses entirely on Nelle. This was done because there wasn't time to fit all of the current material into a single morning and I was concerned that jumping back and forth between examples was confusing.

I prepped this material the day before teaching it, so it's certainly a little rough around the edges. I don't personally have time to take it further at the moment, but Greg asked that I put it up in case someone wanted to clean it up as an alternative to the current material. So, here it is.

The data files and `goodiff` are just copied from the original directories, but I pulled them out so that the directory structure relates properly the the lessons.