Tickit application plugin for Escape-prefixed shortcut keys

 Tickit::App::Plugin::EscapePrefix applies code to a Tickit instance to let it
 handle <Escape>-prefixed shortcut keys, by converting them into the
 equivalent <M-...> modified keys instead.
 .
 Once applied using the /apply method, the plugin will consume any plain
 <Escape> keys typed at the terminal. If another key arrives soon afterwards,
 this key will be consumed and instead a new keypress event emitted that adds
 the "meta" modifier to it. For example, typing <Escape> <a> will instead emit
 the modified key <M-a> to the application. If no subsequent key arrives after
 a timeout of 3 seconds then the modification will not apply.
 .
 While the plugin is still pending anothey keypress to modify, a small
 indicator window will appear in the bottom left of the display, showing ESC-
 in a reverse-video style, to remind the user the keypress is pending.