Required fixes:
- CallbackQuery is now comparable.
- Message.effective_attachment, Message.photo,
Message.new_chat_members, Message.new_chat_photo &
Game.text_entitties semantic fixes - when they are not defined,
return an empty list.
- Docstring fix to Update class.
* Create a Request class which maintains its own connection pool
* When creating a Bot instance a new Request instance will be created if one wasn't supplied.
* Updater is responsible for creating a Request instance if a Bot instance wasn't provided.
* Dispatcher: add method to run async functions without decorator
* Dispatcher can now run as a singleton (allowing run_async decorator to work) as it always did and as multiple instances (where run_async decorator will raise RuntimeError)