move callbacks/observer examples into examples/events/

examples/events/observer/README.md

@@ -0,0 +1,14 @@
+## About
+
+Registers a class as an observer and defines a callback.
+
+## Use
+
+Run the script, then:
+
+-   change GUI parameters to trigger pdirty
+-   press any macrobutton to trigger mdirty
+-   play audio through any bus to trigger ldirty
+-   any midi input to trigger midi
+
+Pressing `<Enter>` will exit.