Refactor and drop py2 support (#49)

* move is_off property to SmartDevice, implement is_on for bulb and use it

* refactor by moving smartbulb and smartplug to their own classes

* drop python2 compatibility, make flake8 happy

* travis: remove 2.7, add 3.6

pyHS100/protocol.py

@@ -1,6 +1,3 @@
-from __future__ import absolute_import
-from __future__ import unicode_literals
-
 import json
 import socket
 import struct