Change source structure

[dbosk]

The structure should be changed. It would be better if each chapter had its own directory. That would make building slides and individual chapter notes easier.

From a long term perspective, it might be interesting to adapt a structure more in line with OpenSecEd, where each topic has its own repo and is included in the course repo. Then this book would change to a course repo and the book would correspond to a release.

[dbosk]

This requires inputx. Or that would at least make things easier.