Update Plugin.GenServer to match the same pattern that Plugin.Supervisor does, remove Omnibot.Plugin

* using Plugin.GenServer now uses Plugin.Base so that is not required
* Remove Omnibot.Plugin because all it did was include Plugin.GenServer
  and Plugin.Base

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

lib/contrib/fortune.ex

@@ -1,5 +1,5 @@
 defmodule Omnibot.Contrib.Fortune do
-  use Omnibot.Plugin
+  use Omnibot.Plugin.GenServer
 
   @fortunes [
     "Reply hazy, try again",

lib/contrib/linkbot.ex

@@ -1,5 +1,5 @@
 defmodule Omnibot.Contrib.Linkbot do
-  use Omnibot.Plugin
+  use Omnibot.Plugin.GenServer
   require Logger
 
   @default_config timeout: 30_000

lib/contrib/markov/markov.ex

@@ -6,9 +6,9 @@ defmodule Omnibot.Contrib.Markov do
   @default_config path: "markov", order: 2, save_every: 5 * 60
 
   @impl true
-  def children(_cfg, _state) do
+  def children(cfg, _state) do
     [{Task, fn ->
-      Stream.timer(1000)
+      Stream.timer(cfg[:save_every] * 1000)
       |> Stream.cycle()
       |> Stream.each(fn _ -> save_chains() end)
       |> Stream.run()

lib/contrib/on_connect.ex

@@ -1,5 +1,5 @@
 defmodule Omnibot.Contrib.OnConnect do
-  use Omnibot.Plugin
+  use Omnibot.Plugin.GenServer
   require Logger
 
   @default_config [channels: :all, commands: []]

lib/core.ex

@@ -1,5 +1,5 @@
 defmodule Omnibot.Core do
-  use Omnibot.Plugin
+  use Omnibot.Plugin.GenServer
   alias Omnibot.State
 
   @default_config [channels: :all]

lib/plugin/gen_server.ex

@@ -1,7 +1,7 @@
 defmodule Omnibot.Plugin.GenServer do
   defmacro __using__([]) do
     quote do
-      alias Omnibot.Plugin
+      use Omnibot.Plugin.Base
       use GenServer 
 
       def start_link(opts) do

lib/plugin/plugin.ex

@@ -1,8 +0,0 @@
-defmodule Omnibot.Plugin do
-  defmacro __using__([]) do
-    quote do
-      use Omnibot.Plugin.Base
-      use Omnibot.Plugin.GenServer
-    end
-  end
-end