This commit adds support to rustbuild to run all documentation tests, basically
running `rustdoc --test` over all our documentation. This also includes support
for running the error index tests.
This wasn't complete (you need a `./configure`), and it is already
documented well in the main README.
Also adds a reference to the books that this also generates.
`prep.js` outputs its own HTML directives, which `pandoc` cannot
recognize when converting the document into LaTeX (this is why the
PDF docs have never been highlighted as of now).
Note that if we were to add the `.rust` class to snippets, we could
probably use pandoc's native highlighting capatibilities i.e. Kate.
