Add lib/plugin that was removed in the last commit, whoops

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

lib/plugin/supervisor.ex

@@ -0,0 +1,40 @@
+defmodule Omnibot.Plugin.Supervisor do
+  defmacro __using__(_opts) do
+    quote do
+      import Omnibot.Plugin.Supervisor
+      alias Omnibot.Plugin
+      use Supervisor
+
+      @behaviour Omnibot.Plugin.Supervisor
+
+      def start_link(opts) do
+        Supervisor.start_link(__MODULE__, opts[:cfg], opts)
+      end
+
+      def init(_cfg) do
+        Supervisor.init(children(), strategy: :one_for_one)
+      end
+
+    end
+  end
+
+  @callback children() :: [any]
+end
+
+# TODO :
+#   - figure out the best way to allow for including of supervisors and agents into a bot module
+#     - have to `use Agent` both places, this is not optimal
+#       - probably just lacks child_spec/1 ?
+#       - Do away with actual Plugin.Agent set of functions (outside of macro),
+#         and make it behaviours + `use Plugin.Agent` instead?
+# Allow for ergonomic supervisor declarations, maybe like:
+#
+# Plugin.supervisor [
+#   SomeAgent,
+#   SomeGenSever,
+#   SomeWorker,
+# ], strategy: one_for_all
+#
+#
+# And it implements all of the stuff for you? This may be too broad for how I'm doing things
+#   - rename MODULES to PLUGINS