Review all the *Client receiver methods in layer3.go. They should
probably either all be receivers, or none.

Add a Reconnect() function.

Eliminate as many uses of Generic as possible.

Rename extension.StanzaHandlers to something like StanzaTypes.

Think about how to gracefully shutdown. Probably have a Close()
function.

Get rid of logging. We're providing status updates. Allow some sort of
debug flag that prints from layer1.