Optimize I/O access (#59)

* Optimize I/O access

A single update() will now fetch information from all interesting modules,
including the current device state and the emeter information.

In practice, this will allow dropping the number of I/O reqs per homeassistant update cycle to 1,
which is paramount at least for bulbs which are very picky about sequential accesses.
This can be further extend to other modules/methods, if needed.

Currently fetched data:
* sysinfo
* realtime, today's and this months emeter stats

New properties:
* emeter_realtime: return the most recent emeter information, update()-version of get_emeter_realtime()
* emeter_today: returning today's energy consumption
* emeter_this_month: same for this month

Other changes:
* Accessing @requires_update properties will cause SmartDeviceException if the device has not ever been update()d
* Fix __repr__ for devices that haven't been updated
* Smartbulb uses now the state data from get_sysinfo instead of separately querying the bulb service
* SmartStrip's state_information no longer lists onsince for separate plugs
* The above mentioned properties are now printed out by cli
* Simplify is_on handling for bulbs

* remove implicit updates, return device responses for actions, update README.md instructions. fixes #61

kasa/smartplug.py

@@ -50,16 +50,14 @@ class SmartPlug(SmartDevice):
 
         :raises SmartDeviceException: on error
         """
-        await self._query_helper("system", "set_relay_state", {"state": 1})
-        await self.update()
+        return await self._query_helper("system", "set_relay_state", {"state": 1})
 
     async def turn_off(self):
         """Turn the switch off.
 
         :raises SmartDeviceException: on error
         """
-        await self._query_helper("system", "set_relay_state", {"state": 0})
-        await self.update()
+        return await self._query_helper("system", "set_relay_state", {"state": 0})
 
     @property  # type: ignore
     @requires_update
@@ -78,8 +76,9 @@ class SmartPlug(SmartDevice):
         :param bool state: True to set led on, False to set led off
         :raises SmartDeviceException: on error
         """
-        await self._query_helper("system", "set_led_off", {"off": int(not state)})
-        await self.update()
+        return await self._query_helper(
+            "system", "set_led_off", {"off": int(not state)}
+        )
 
     @property  # type: ignore
     @requires_update