Classification

Apologies if you've been having trouble downloading the book for the last couple of days. I think I've sorted this out now, but let me know if you have trouble with time-outs or whatever. In the meantime I've made all of the figures for the classification chapter and am now rewriting the text so that it is slightly more comprehensible. I've also written a draft preface and added an acknowledgements section, so if you mail me errata you will see your name added to this.