This allows and includes better flow control handling for QoS>0.

Thanks to Matt Ingenthron.

Closes #1212.

Thanks to Ben Barbour.

Closes #1220.

Add ALPN support for all clients, update documentation, and add to ChangeLog.

Bridge TLS Application-Layer Protocol Negotiation

This needs a lot of improvement, but is a reasonable start.

Logically dead code.

In order to connect to brokers that support both websockets and
mqtt on the same port (such as Amazon IoT), we need to set an
application for the SSL context.  This change allows the specification
of an application by using the `bridge_alpn` configuration token.

Signed-off-by: John Hickey <jjh-github@daedalian.us>