Simplify API documentation by using doctests (#73)

* Add doctests to SmartBulb

* Add SmartDevice doctests, cleanup README.md

* add doctests for smartplug and smartstrip

* add discover doctests

* Fix bulb mock

* add smartdimmer doctests

* add sphinx-generated docs, cleanup readme a bit

* remove sphinx-click as it does not work with asyncclick

* in preparation for rtd hooking, move doc deps to be separate from dev deps

* pytestmark needs to be applied separately for each and every file, this fixes the tests

* use pathlib for resolving relative paths

* Skip discovery doctest on python3.7

The code is just fine, but some reason the mocking behaves differently between 3.7 and 3.8.
The latter seems to accept a discrete object for asyncio.run where the former expects a coroutine..

kasa/tests/fixtures/KL130(US)_1.0.json

@@ -27,7 +27,7 @@
     "system": {
         "get_sysinfo": {
             "active_mode": "none",
-            "alias": "Nick office tplink",
+            "alias": "KL130 office bulb",
             "ctrl_protocols": {
                 "name": "Linkie",
                 "version": "1.0"
@@ -45,7 +45,7 @@
             "is_factory": false,
             "is_variable_color_temp": 1,
             "light_state": {
-                "brightness": 0,
+                "brightness": 30,
                 "color_temp": 0,
                 "hue": 15,
                 "mode": "normal",