Add classes for broker types

[AlanCoding]

I started this out adding methods like publish_message as static methods, because static methods are simpler. But this has gotten more complicated with connection management.

Ultimately, the "producer" probably shouldn't own the connection, and the broker should own it.

For this to make sense, the "broker" should be class-based. It will have 2 versions, an async and synchronous version.

[AlanCoding]

Oh, this was done in the config work #64