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;

include/ftxui/component/receiver.hpp

@@ -51,6 +51,8 @@ class SenderImpl {
   void Send(T t) { receiver_->Receive(std::move(t)); }
   ~SenderImpl() { receiver_->ReleaseSender(); }
 
+  Sender<T> Clone() { return receiver_->MakeSender(); }
+
  private:
   friend class ReceiverImpl<T>;
   SenderImpl(ReceiverImpl<T>* consumer) : receiver_(consumer) {}
@@ -61,6 +63,7 @@ template <class T>
 class ReceiverImpl {
  public:
   Sender<T> MakeSender() {
+    std::unique_lock<std::mutex> lock(mutex_);
     senders_++;
     return std::unique_ptr<SenderImpl<T>>(new SenderImpl<T>(this));
   }