v0.24.0: Bump version to 0.24.0

I used a specially modified version of the publish script to avoid
bumping the `witx` version.

v0.23.0: Bump version to 0.23.0

I used a specially modified version of the publish script to avoid
bumping the `witx` version.

v0.22.1

Bump smallvec dependency to 1.6.1

v0.22.0: Merge pull request #2557 from fitzgen/wasmtime-0.22.0

Wasmtime 0.22.0

v0.21.0

Bump to 0.21.0 (#2359)

v0.20.0

Add metadata to peepmatic crates (#2245)

v0.19.0: Wasmtime 0.19.0 and Cranelift 0.66.0 (#2027)

This commit updates Wasmtime's version to 0.19.0, Cranelift's version to
0.66.0, and updates the release notes as well.

v0.18.0

Wasmtime 0.18.0 and Cranelift 0.65.0.

v0.16.0

Update release notes, wasmtime 0.16, cranelift 0.63.

0.15.0

v0.15.0

Update the env var name in more places.