Everything relevant is in the repo description, git history and `cargo doc`.

# Features

- `nightly`: Is required for `ptr_metadata`.
- `specialization`: Useful for certain optimizations like a bitwise copy of `[impl Copy]` while allowing cloning each item of `[impl Clone]`.
- `allocator_api`: Enables usage of <https://doc.rust-lang.org/unstable-book/library-features/allocator-api.html>.