Changes in v1.1
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* Additional handler type: Keys handler
* Menuitem handlers now have a return value of type t_handler_return.
  For all simple cases, you just return ACTION_VALID or ACTION_INVALID
  (For some types of menu items, handlers are ignored, and for 
   others the return value is ignored)
* add_menu takes an extra argument (to better control memory footprint)
  You can just set it to -1 to choose the default value
* Now the menu system support long menu's using scroll bars.
* Support for passwords and context sensitive help is added.