* Use the map form for transport options everywhere
* Remove mentions of the list form for transport options
* Use a state enter call instead of gen_statem:enter_loop/4 and
  proc_lib:start_link/3 in the tcp_reverse example
* Take care of different EOLs in the tcp_reverse example
* Mention state enter calls, the next_event action, and {continue, ...}
  in the docs for how to use gen_statem and gen_server

This commit deprecates Transport:accept_ack/1 in favor of
a new forward-compatible function. Transport:handshake/1,2
will use ssl:handshake/2,3 from Ranch 2.0 onward.

Also improves the good example a little by using spawn_link
instead of start_link.