Add Sphinx API doc generation (#3029)

* add's sphinx project to docs/ dir
* include core/helpers autodocs for API reference

docs/source/api/core.rst

@@ -0,0 +1,18 @@
+.. _core_module:
+
+:mod:`homeassistant.core`
+-------------------------
+
+.. automodule:: homeassistant.core
+
+.. autoclass:: Config
+    :members:
+
+.. autoclass:: EventBus
+    :members:
+
+.. autoclass:: StateMachine
+    :members:
+
+.. autoclass:: ServiceRegistry
+    :members:

docs/source/api/entity.rst

@@ -0,0 +1,12 @@
+.. _helpers_entity_module:
+
+:mod:`homeassistant.helpers.entity`
+-----------------------------------
+
+.. automodule:: homeassistant.helpers.entity
+
+.. autoclass:: Entity
+    :members:
+
+.. autoclass:: ToggleEntity
+    :members:

docs/source/api/event.rst

@@ -0,0 +1,20 @@
+.. _helpers_event_module:
+
+:mod:`homeassistant.helpers.event`
+----------------------------------
+
+.. automodule:: homeassistant.helpers.event
+
+.. autofunction:: track_state_change
+
+.. autofunction:: track_point_in_time
+
+.. autofunction:: track_point_in_utc_time
+
+.. autofunction:: track_sunrise
+
+.. autofunction:: track_sunset
+
+.. autofunction:: track_utc_time_change
+
+.. autofunction:: track_time_change