Signed-off-by: Le Tan <tamlokveer@gmail.com>
1. Add menu item "Converter" to choose markdown converter; 2. Add menu item "About" and "About Qt"; 3. Change all QMessageBox's parent to "this"; Signed-off-by: Le Tan <tamlokveer@gmail.com>
Make it convenient to add third-party libraries. Signed-off-by: Le Tan <tamlokveer@gmail.com>