新增可解锁Hold机制并补全特殊强化提示

src/source/Tetris.cpp

@@ -369,6 +369,10 @@ LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
                 DeleteLines();
             }
             break;
+        case 'C':
+        case VK_SHIFT:
+            HoldCurrentPiece();
+            break;
         default:
             break;
         }