* Addressing #473 ... if I understood the ticket right, we want to pass through whatever the application provides as a topic identifier, leaving hashing (or not hashing) up to the application.
* Remove TopicDescriptor and use Topic newtype everywhere
* PR feedback
Use From<Topic> instead of Into<String>
Use impl Into<Topic> instead of Topic in public API
Co-authored-by: Peat Bakke <peat@peat.org>