This matters because if 'a were free to choose, then the argument would
be trivial. But in reality the argument also holds if 'a was already
chosen, which is what makes lifetimes special.
This reverts commit 7f1d1c6d9a7be5e427bace30e740b16b25f25c92.
The original commit was created because mdBook and rustdoc had
different generation algorithms for header links; now with
https://github.com/rust-lang/rust/pull/39966 , the algorithms
are the same. So let's undo this change.
... when I came across this problem, I said "eh, this isn't fun,
but it doesn't take that long." I probably should have just actually
taken the time to fix upstream, given that they were amenable. Oh
well!
mdbook has a lot of optional dependencies that we don't want, so instead
of using it directly, we re-build rustbook to use mdbook as a library.
For convenience' sake, we keep the same CLI interface as mdbook; the
only difference is that it only accepts build and test subcommands,
rather than the full range.