0.5.7

Chore

• update protobuf to 2.17.0 (#783) (af5234d4, closes #782)

Bug Fixes

• Avoid implicit transactions in DbTransactionPool (#777) (e0448583, closes #768)

Features

• switch spanner's db pool to deadpool (077bf091)
• emit internal bb8 Pool errors to logs/sentry (ec25bc47, closes #786, #785, #764, #787)

Refactor

• cleanup/rearrange (7e526cb8)