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/smartdimmer.py

@@ -60,10 +60,9 @@ class SmartDimmer(SmartPlug):
         if not isinstance(value, int):
             raise ValueError("Brightness must be integer, " "not of %s.", type(value))
         elif 0 <= value <= 100:
-            await self._query_helper(
+            return await self._query_helper(
                 "smartlife.iot.dimmer", "set_brightness", {"brightness": value}
             )
-            await self.update()
         else:
             raise ValueError("Brightness value %s is not valid." % value)