2. Add exception handling to EditorWindow Tkinter variable setvar() and getvar() fcns.
3. EditorWindow: remove some unneeded comments.
4. Add a separator to the Options menu
5. extend.txt: describe how to create a menu entry which has no keybinding.
M Bindings.py
M EditorWindow.py
M extend.txt
Extensions must still be configured manually and there is currently one
set of extension key bindings for all platforms.
Bring NEWS.txt up to date.
Update CREDITS.txt and idlever.py for release.
M NEWS.txt
M config-extensions.def
M extend.txt
M help.txt
M idlever.py
