Cargo: version 0.2.0 -> 0.3.0

[cpu]

This branch prepares a 0.3.0 release, primarily to publish the rustls update (#70)

Proposed release notes

• Updates Rustls from 0.22 to 0.23.

Post-merge steps

• Generate Android Maven artifacts locally - N/A - no non-test changes made under android/
• Create and push Git tag - created v/0.3.0 tag
• cargo publish for each required crate, based on release steps - Published rustls-platform-verifier v0.3.0 at registry crates-io
• Create companion GitHub release - created v/0.3.0 release

[cpu]

Released!