The screencast plugin is complete (for now)

[Edward K. Ream]

As of rev 5458, the screencast plugin should be usable in most situations.  Recent work:

- At last I am satisfied with the docstring.

- Added m.open_menu method.  These took a lot of work.  From the reference part of the docstring:

QQQ
**m.open_menu(menu_name)** Opens the menu whose name is given, ignoring case and any non-alpha characters in menu_name. This method shows all parent menus, so m.open_menu('cursorback') suffices to show the "Cmds\:Cursor/Selection\:Cursor Back..." menu.
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This method is important.  It will make life a lot easier for presenters:  no more futzing with the mouse during presentations!

There is one slight glitch.  The presenter can't go on to the next slide until they have dismissed the menus with one or more presses of the Escape key.  The reason is straightforward: the menu grabs all keystrokes until it is dismissed.  Formerly, the presenter had to be careful not to hit Escape once to often: doing so would quit the screencast!  To handle this, Escape now goes to the next slide, just like RtArrow.  So the only way to quit a slideshow is to do Ctrl-G.  You can see the behavior in action by starting @screencast menus in test.leo.

Now that the screencast plugin itself is complete, the next step will be to create more screencasts.  It's possible that more features or "jiggles" will be needed in the plugin, but I think it will stand up pretty well.  Please use the plugin and let me know what you think.

Edward