0.2.0 release preparation

[cpu]

Proposed initial CHANGELOG entry:

• Rustls version updated from 0.21 to 0.22

These are the steps remaining for the release after this merges:

• Generate the Android Maven artifacts (N/A - no android/ changes)
• Create rel-0.2 branch (https://github.com/rustls/rustls-platform-verifier/tree/rel-0.2)
• Create Git tag
• Push tag - https://github.com/rustls/rustls-platform-verifier/releases/tag/v%2F0.2.0
• cargo publish (--allow-dirty may be needed based on the above) - Published rustls-platform-verifier v0.2.0 at registry crates-io
• Create companion GitHub release - https://github.com/rustls/rustls-platform-verifier/releases/tag/v%2F0.2.0

[cpu]

All finished! 0.2.0 is now available on Crates.io, and a GitHub release has been created.