**Compatibility**:
* Ensures compatibility with Rust 1.40.0 through 1.72.1. This bumps the
minimum supported Rust version from 1.16 to 1.40.
Changes:
* Soundness: Wrap writes to uninitialized memory in `mem::MaybeUninit`.
The unsoundness was present in all versions since 0.2.0. There is no
evidence that rustc took advantage of the unsoundness to compile
programs in a problematic way.
Thanks to Cam Lloyd for originally contributing these changes, and
thanks to Maxwell McKinnon for rebasing them on top of 3.5.0.