- added docs and examples for bpy.app.handlers

- correct error in own last commit for BKE_screen_find_big_area()

doc/python_api/examples/bpy.app.handlers.py

@@ -0,0 +1,12 @@
+"""
+Basic Handler Example
++++++++++++++++++++++
+This script shows the most simple example of adding a handler.
+"""
+
+import bpy
+
+def my_handler(scene):
+   print("Frame Change", scene.frame_current)
+
+bpy.app.handlers.frame_change_pre.append(my_handler)