Fix parsing of keys that are prefix of others. (#58)

The ESC key generates sequences that are prefix of others. For instance:
- ESC => [27]
- F1 =>  [27, 79, 8]

As a result, we can't generate the ESC event when receiving [27],
because it might be the start of the [27, 79, 8] sequence (or not).

Application usually applies a timeout to help detecting the ESC key.
This patch introduce a timeout. It is set to 50ms.

Bug: https://github.com/ArthurSonzogni/FTXUI/issues/55

include/ftxui/component/event.hpp

@@ -23,8 +23,6 @@ struct Event {
   static Event Character(const std::string&);
   static Event Special(const std::string&);
 
-  static void Convert(Receiver<char>& in, Sender<Event>& out, char c);
-
   // --- Arrow ---
   static const Event ArrowLeft;
   static const Event ArrowRight;