Further separate module agents and module impl

Add Omnibot.Module.Agent which implements the basic agent cfg + state
persistence functionality, which is then included in the Omnibot.Module.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

lib/module/module.ex

@@ -2,28 +2,7 @@ defmodule Omnibot.Module do
   defmacro __using__([]) do
     quote do
       use Omnibot.Module.Base
-      use Agent
-
-      def start_link(opts) do
-        cfg = opts[:cfg]
-        Agent.start_link(fn -> {cfg, on_init(cfg)} end, opts ++ [name: __MODULE__])
-      end
-
-      def cfg do
-        Agent.get(__MODULE__, fn {cfg, _} -> cfg end)
-      end
-
-      def state do
-        Agent.get(__MODULE__, fn {_, state} -> state end)
-      end
-
-      def update_state(update, timeout \\ 5000) do
-        Agent.update(
-          __MODULE__,
-          fn {cfg, state} -> {cfg, apply(update, [state])} end,
-          timeout
-        )
-      end
+      use Omnibot.Module.Agent
     end
   end
 end