Improve emeterstatus API, move into own module (#205)

Adds the following properties to EmeterStatus for saner API:
* voltage (in V)
* power (in W)
* current (in A)
* total (in kWh)

kasa/smartbulb.py

@@ -3,12 +3,7 @@ import logging
 import re
 from typing import Any, Dict, NamedTuple, cast
 
-from kasa.smartdevice import (
-    DeviceType,
-    SmartDevice,
-    SmartDeviceException,
-    requires_update,
-)
+from .smartdevice import DeviceType, SmartDevice, SmartDeviceException, requires_update
 
 
 class ColorTempRange(NamedTuple):