This primary fix brought on by this upgrade is the proper matching of the ```
and ~~~ doc blocks. This also moves hoedown to a git submodule rather than a
bundled repository.
Additionally, hoedown is stricter about code blocks, so this ended up fixing a
lot of invalid code blocks (ending with " ```" instead of "```", or ending with
"~~~~" instead of "~~~").
Closes#12776
This is in preparation to remove the implementations of ToStrRadix in integers, and to remove the associated logic from `std::num::strconv`.
The parts that still need to be liberated are:
- `std::fmt::Formatter::runplural`
- `num::{bigint, complex, rational}`
