Add support for additional keys (#140)

Author: ProjektGopher

src/Key.php

@@ -6,8 +6,12 @@ class Key
 {
     const UP = "\e[A";
 
+    const SHIFT_UP = "\e[1;2A";
+
     const DOWN = "\e[B";
 
+    const SHIFT_DOWN = "\e[1;2B";
+
     const RIGHT = "\e[C";
 
     const LEFT = "\e[D";
@@ -20,6 +24,8 @@ class Key
 
     const LEFT_ARROW = "\eOD";
 
+    const ESCAPE = "\e";
+
     const DELETE = "\e[3~";
 
     const BACKSPACE = "\177";