add popup menu to allow python scripts to show popups without having to define a menu class first.

doc/python_api/examples/bpy.types.WindowManager.popup_menu.py

@@ -0,0 +1,14 @@
+"""
+Popup Menus
++++++++++++
+Popup menus can be useful for creating menus without having to register menu classes.
+
+Note that they will not block the scripts execution, so the caller can't wait for user input.
+"""
+
+import bpy
+
+def draw(self, context):
+    self.layout.label("Hello World")
+
+bpy.context.window_manager.popup_menu(draw, title="Greeting", icon='INFO')