Handshake refactor

[mmmries]

While working on #37 I was bugged by the fact that we had several functions in the Gnat module that were only useful for the handshake. I thought it would be nicer to let all of the handshake logic happen in its own module with just a simple {:ok, socket} or {:error, reason} return value.

I also didn't like constantly having to to do

socket_write(state.connection_settings, state.socket, "PING\r\n")

So I changed the socket_write and socket_close functions to just accept the entire state as the first argument and it extracts the options/socket as needed.

socket_write(state, "PING\r\n")

/cc @quixoten @film42 @newellista @jjcarstens @tallguy-hackett

[quixoten]

👍

[film42]

I'm not sure what kind of guarantees socket write has, but it might be better to queue these messages up in the event that your kernel's buffer fills. Ex: PING\r\n and PONG\r\n.