v0.8.0

What's Changed

• update gradle/java/kotlin/grpc/proto by @piercetrey-figure in #21
• use pb-grpc-client-kotlin by @piercetrey-figure in #22
• use shared channel for PbClient to allow for proper shutdown by @piercetrey-figure in #23

Full Changelog: v0.7.0...v0.8.0