Update to Bot API 5.0, add rake tasks for deleteWebhook, close & logOut

lib/telegram/bot.rb

@@ -28,6 +28,7 @@ module Telegram
     autoload :Initializers,       'telegram/bot/initializers'
     autoload :Middleware,         'telegram/bot/middleware'
     autoload :RSpec,              'telegram/bot/rspec'
+    autoload :Tasks,              'telegram/bot/tasks'
     autoload :UpdatesController,  'telegram/bot/updates_controller'
     autoload :UpdatesPoller,      'telegram/bot/updates_poller'
   end