Add H, M, L commands to move cursor within screen

src/core/Command.h

@@ -42,6 +42,9 @@ public:
         GO_RIGHT,
         GO_START_OF_LINE,
         GO_END_OF_LINE,
+        GO_TOP_OF_SCREEN,
+        GO_MIDDLE_OF_SCREEN,
+        GO_BOTTOM_OF_SCREEN,
         NEXT,
         PREV,
         SCROLL_WINDOW_UP_ONE_LINE,