Creating lesson on csv read write

This lesson should be finished and ready for review. I removed the inline tables from the end of the lesson, as these were meant to show the same thing as the figures that I was having trouble embedding (but that JB successfully embedded).
If the goal is teaching them to check for problems with the data, why not just use `unique` or `table` to demonstrate how to find unexpected variables? Since `tapply` is more advanced, you would have to spend a bunch of time explaining how it works when the only thing it adds is getting the means, which you don't use for anything else later in the lesson.