Consider folding Bunny::Transport into Bunny::Session

[michaelklishin]

Bunny::Transport was originally introduced to separate Bunny::Session, a part of the original 2009 design, from the 2 socket implementations (MRI, JRuby) x two socket types ("plain" TCP, TLS).

As of #701 #702, this layer layer is likely unnecessary and Bunny::Transport can be merged with Bunny::Session.

Backwards Compatibility Considerations

c = Bunny.new
c.transport.configure_socket |socket|
end

can be reimplemented by making Bunny::Session#transport return self.