This changes `with_renderer` and `with_preprocessor` to replace any
extensions of the same name instead of just appending to the list. This
is necessary for rust-lang's build process, because we replace the
preprocessors with local ones. Previously, mdbook would just print an
error, but continue working. With the change that preprocessors are no
longer optional by default, it is now required that we have a way to
replace the existing entries.
This removes toml as a public dependency. This reduces the exposure of
the public API, reduces exposure of internal implementation, and makes
it easier to make semver-incompatible changes to toml.
This is accomplished through a variety of changes:
- `get` and `get_mut` are removed.
- `get_deserialized_opt` is renamed to `get`.
- Dropped the AsRef for `get_deserialized_opt` for ergonomics, since
using an `&` for a String is not too much to ask, and the other
generic arg needs to be specified in a fair number of situations.
- Removed deprecated `get_deserialized`.
- Dropped `TomlExt` from the public API.
- Removed `get_renderer` and `get_preprocessor` since they were trivial
wrappers over `get`.
