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/index.rst

@@ -0,0 +1,22 @@
+===============
+Handling events
+===============
+
+*aiogram* imcludes Dispatcher mechanism. 
+Dispatcher is needed for handling incoming updates from Telegram.
+
+With dispatcher you can do:
+
+- Handle incoming updates;
+- Filter incoming events before it will be processed by specific handler;
+- Modify event and related data in middlewares;
+- Separate bot functionality between different handlers, modules and packages
+
+Dispatcher is also separated into two entities - Router and Dispatcher.
+Dispatcher is subclass of router and should be always is root router.
+
+.. toctree::
+
+    observer
+    router
+    dispatcher