Improve docs for crate features

The `chrono` crate makes use of several Cargo features:
https://github.com/chronotope/chrono/blob/02c68d69a1ff8e6461384a770b87737b5096eae3/Cargo.toml#L19-L46

These features are documented in both `README.md` and the rustdocs
in `lib.rs, however, the lists in each place were missing some features
and also inconsistent in their descriptions.

I've also removed the unused `[wasm-bindgen]` link definition.

Fixes #1434.

README.md

@@ -50,21 +50,31 @@ See [docs.rs](https://docs.rs/chrono/latest/chrono/) for the API reference.
 
 Default features:
 
-* `alloc`: Enable features that depend on allocation (primarily string formatting)
+* `alloc`: Enable features that depend on allocation (primarily string formatting).
 * `std`: Enables functionality that depends on the standard library. This is a superset of `alloc`
   and adds interoperation with standard library types and traits.
 * `clock`: Enables reading the local timezone (`Local`). This is a superset of `now`.
-* `now`: Enables reading the system time (`now`)
+* `now`: Enables reading the system time (`now`).
 * `wasmbind`: Interface with the JS Date API for the `wasm32` target.
 
 Optional features:
 
-* `serde`: Enable serialization/deserialization via serde.
-* `rkyv`: Enable serialization/deserialization via rkyv.
+* `serde`: Enable serialization/deserialization via [serde].
+* `rkyv`: Deprecated, use the `rkyv-*` features.
+* `rkyv-16`: Enable serialization/deserialization via [rkyv], using 16-bit integers for integral `*size` types.
+* `rkyv-32`: Enable serialization/deserialization via [rkyv], using 32-bit integers for integral `*size` types.
+* `rkyv-64`: Enable serialization/deserialization via [rkyv], using 64-bit integers for integral `*size` types.
+* `rkyv-validation`: Enable rkyv validation support using `bytecheck`.
 * `rustc-serialize`: Enable serialization/deserialization via rustc-serialize (deprecated).
-* `arbitrary`: construct arbitrary instances of a type with the Arbitrary crate.
+* `arbitrary`: Construct arbitrary instances of a type with the Arbitrary crate.
 * `unstable-locales`: Enable localization. This adds various methods with a `_localized` suffix.
   The implementation and API may change or even be removed in a patch release. Feedback welcome.
+* `oldtime`: This feature no longer has any effect; it used to offer compatibility with the `time` 0.1 crate.
+
+Note: The `rkyv{,-16,-32,-64}` features are mutually exclusive.
+
+[serde]: https://github.com/serde-rs/serde
+[rkyv]: https://github.com/rkyv/rkyv
 
 ## Rust version requirements
 

src/lib.rs

@@ -24,30 +24,35 @@
 //!
 //! Default features:
 //!
-//! - `alloc`: Enable features that depend on allocation (primarily string formatting)
+//! - `alloc`: Enable features that depend on allocation (primarily string formatting).
 //! - `std`: Enables functionality that depends on the standard library. This
 //!   is a superset of `alloc` and adds interoperation with standard library types
 //!   and traits.
-//! - `clock`: Enables reading the system time (`now`) that depends on the standard library for
-//! UNIX-like operating systems and the Windows API (`winapi`) for Windows.
+//! - `clock`: Enables reading the local timezone (`Local`). This is a superset of `now`.
+//! - `now`: Enables reading the system time (`now`).
 //! - `wasmbind`: Interface with the JS Date API for the `wasm32` target.
 //!
 //! Optional features:
 //!
-//! - [`serde`][]: Enable serialization/deserialization via serde.
-//! - `rkyv`: Enable serialization/deserialization via rkyv.
-//! - `arbitrary`: construct arbitrary instances of a type with the Arbitrary crate.
+//! - `serde`: Enable serialization/deserialization via [serde].
+//! - `rkyv`: Deprecated, use the `rkyv-*` features.
+//! - `rkyv-16`: Enable serialization/deserialization via [rkyv], using 16-bit integers for integral `*size` types.
+//! - `rkyv-32`: Enable serialization/deserialization via [rkyv], using 32-bit integers for integral `*size` types.
+//! - `rkyv-64`: Enable serialization/deserialization via [rkyv], using 64-bit integers for integral `*size` types.
+//! - `rkyv-validation`: Enable rkyv validation support using `bytecheck`.
+//! - `rustc-serialize`: Enable serialization/deserialization via rustc-serialize (deprecated).
+//! - `arbitrary`: Construct arbitrary instances of a type with the Arbitrary crate.
 //! - `unstable-locales`: Enable localization. This adds various methods with a
 //!   `_localized` suffix. The implementation and API may change or even be
 //!   removed in a patch release. Feedback welcome.
-//! - `oldtime`: this feature no langer has a function, but once offered compatibility with the
-//!   `time` 0.1 crate.
+//! - `oldtime`: This feature no longer has any effect; it used to offer compatibility with the `time` 0.1 crate.
 //!
-//! [`serde`]: https://github.com/serde-rs/serde
-//! [wasm-bindgen]: https://github.com/rustwasm/wasm-bindgen
+//! Note: The `rkyv{,-16,-32,-64}` features are mutually exclusive.
 //!
-//! See the [cargo docs][] for examples of specifying features.
+//! See the [cargo docs] for examples of specifying features.
 //!
+//! [serde]: https://github.com/serde-rs/serde
+//! [rkyv]: https://github.com/rkyv/rkyv
 //! [cargo docs]: https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#choosing-features
 //!
 //! ## Overview