Upgrade architecture + 5.0 Bot API (#469)

Upgrade architecture + 5.0 Bot API (#469)
* Moved `methods`, `types` and `client` to root package
* Removed update handler from routers to dispatcher
* Reworked events propagation mechanism to handlers
* Reworked inner middlewares logic (very small change)
* Updated to Bot API 5.0
* Initial migration from MkDocs to Sphinx + config for readthedocs

docs2/dispatcher/observer.rst

@@ -0,0 +1,26 @@
+########
+Observer
+########
+
+Observer is used for filtering and handling different events. That is part of internal API with some public methods and is recommended to don't use methods is not listed here.
+
+In `aiogram` framework is available two variants of observer:
+
+- `EventObserver <#eventobserver>`__ 
+- `TelegramEventObserver <#telegrameventobserver>`__
+
+
+EventObserver
+=============
+
+.. autoclass:: aiogram.dispatcher.event.event.EventObserver
+    :members: register, trigger, __call__
+    :member-order: bysource
+
+
+TelegramEventObserver
+=====================
+
+.. autoclass:: aiogram.dispatcher.event.telegram.TelegramEventObserver
+    :members: register, trigger, __call__, bind_filter, middleware, outer_middleware
+    :member-order: bysource