Add retries to protocol queries (#65)

* Add retries to query(), defaults to 3 + add tests

* Catch also json decoding errors for retries

* add missing exceptions file, fix old protocol tests

kasa/exceptions.py

@@ -0,0 +1,5 @@
+"""python-kasa exceptions."""
+
+
+class SmartDeviceException(Exception):
+    """Base exception for device errors."""