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

src/ftxui/component/terminal_input_parser.hpp

@@ -0,0 +1,48 @@
+#ifndef FTXUI_COMPONENT_TERMINAL_INPUT_PARSER
+#define FTXUI_COMPONENT_TERMINAL_INPUT_PARSER
+
+#include "ftxui/component/event.hpp"
+#include "ftxui/component/receiver.hpp"
+
+#include <string>
+
+namespace ftxui {
+
+// Parse a sequence of |char| accross |time|. Produces |Event|.
+class TerminalInputParser {
+ public:
+  TerminalInputParser(Sender<Event> out);
+  void Timeout(int time);
+  void Add(char c);
+
+ private:
+  unsigned char Current();
+  bool Eat();
+
+  enum Type {
+    UNCOMPLETED = 0,
+    DROP = 1,
+    CHARACTER = 2,
+    SPECIAL = 3,
+  };
+  void Send(Type type);
+  Type Parse();
+  Type ParseUTF8();
+  Type ParseESC();
+  Type ParseDCS();
+  Type ParseCSI();
+  Type ParseOSC();
+
+  Sender<Event> out_;
+  int position_ = -1;
+  int timeout_ = 0;
+  std::string pending_;
+};
+
+}  // namespace ftxui
+
+#endif /* end of include guard: FTXUI_COMPONENT_TERMINAL_INPUT_PARSER */
+
+// Copyright 2020 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.