There is likely to be new users with the alpha release, and there are a lot of documents on the internet (StackOverflow, reddit, blogs) that refer to these guides, so emitting a more helpful error than "404" is nice. Hence, I've temporarily reinstated stub documents for each of the old guides, referring to as relevant a part of the book as possible.
Also, rustbook was silently ignoring some errors, which lead to an inconsistency with directory creation/file writing. This meant the CSS file was not being written if no `doc` directory existed in the users build dir (e.g. the buildbots). This should mean that the CSS will appear automatically in later builds.
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