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`.
This updates everything for the move of utils to mdbook-core. There will
be followup commits that will be moving and refactoring these utils.
This simply moves them over unchanged (except visibility).
This is a pure git rename in order to make sure that git can follow
history. The next commit will integrate these into mdbook-core.
Additional commits will refactor/move/remove items.
