What's Changed
The 0.15.12 release was yanked after it turned out to be semver-incompatible with existing usage by several of the most popular dependent crates, because it introduced a std feature -- and those crates used default-features = false but relied on the std-guarded features.
The 0.16.0 API should be semver-compatible with the 0.15.x API except for the need for the std feature.
Refer to the 0.15.12 release notes for more information.