There are hundreds of stackoverflow answers, reddit posts and blog
articles that link to these documents, so it's a nicer user experience
if they're not plain 404s.
The intention is to let these hang around only for relatively short
while. The alpha is likely to bring in many new users and they will be
reading the documents mentioned above.
This pulls all of our long-form documentation into a single document,
nicknamed "the book" and formally titled "The Rust Programming
Language."
A few things motivated this change:
* People knew of The Guide, but not the individual Guides. This merges
them together, helping discoverability.
* You can get all of Rust's longform documentation in one place, which
is nice.
* We now have rustbook in-tree, which can generate this kind of
documentation. While its style is basic, the general idea is much
better: a table of contents on the left-hand side.
* Rather than a almost 10,000-line guide.md, there are now smaller files
per section.
