Open
Description
javadoc includes helpful @since and @deprecated tags to document API changes. We regularly make breaking changes in this library, but don't have a convention for documenting deprecated code except for logging a deprecation warning.
Since we're committed to maintaining each published version of the API up to 18 months after the v1 release, we should make it easy for users to see which versions of the library include which features, and to tell what changes (if any) they'd need to make to their code to upgrade to a newer version of opencensus.
Consider using the deprecated library for deprecations, and doing something similar to denote when new features are added to the API.
cc @songy23, @rghetia, @dinooliva