Run an Elixir or Erlang shell as a GenServer process

# Installation

Install `extty` by adding it to your list of dependencies in `mix.exs`:

def deps() do
    {:extty, "~> 0.2"}

# Usage

This is heavily adapted from [`ssh_cli.erl`](
and functions much like the SSH console implementation.

This will start a terminal shell process in a GenServer. You can then send ANSI text
to it to behave like a normal TTY. When starting the shell, you must specify a handler
pid to receive the returned text data. The incoming message will be formatted as
`{:tty_data, String.t()}`


iex()> {:ok, tty} = ExTTY.start_link(handler: self())
iex()> flush()
{:tty_data, "Interactive Elixir (1.10.3) - press Ctrl+C to exit (type h() ENTER for help)\r\n"}
{:tty_data, "iex(1)> "}
iex()> ExTTY.send_text(tty, "1+1\n")
iex()> flush()
{:tty_data, "1+1\r\n"}
{:tty_data, "\e[33m2\e[0m\r\n"}
{:tty_data, "iex(2)> "}