Just a few weeks back, Mariupol was a bustling city in south-eastern Ukraine, overlooking the Sea of Azov. Home to just under half a million people.   Now, it is basically no more.   Most people’s homes have been destroyed. Half the city has fled and even those who have managed to leave have faced a treacherous journey to some form of safety.   Our International Editor Lindsey Hilsum has spoken to dozens of survivors from Mariupol, to tell their story and provide evidence of atrocities that many believe are war crimes.