The terminal has changed its size, most likely because the user has resized the window. This callback is
invoked by something inside the lanterna library, it could be a signal handler thread, it could be the AWT
thread, it could be something else, so please be careful with what kind of operation you do in here. Also,
make sure not to take too long before returning. Best practice would be to update an internal status in your
program to mark that the terminal has been resized (possibly along with the new size) and then in your main
loop you deal with this at the beginning of each redraw.