This removes the `pub` status of the SectionNumber field. The intent is
to make this potentially extensible in the future if we decide to add
more fields, or change its internal representation. With the existence
of the deref impls, generally this change shouldn't be visible except
for the constructor, which hopefully shouldn't be too cumbersome to use
`SectionNumber::new` instead.
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`.
