BEIRUT (Reuters) - Syrian government forces killed 21 people around the country on Friday, activists said, with at least nine people killed by tank shelling in opposition districts of the central city of Homs. The resumption of heavy shelling comes after a few days of relative calm during which U.N. humanitarian chief Valerie Amos visited Homs and said part of the city had been completely destroyed. The Baba Amr district was besieged and shelled for a month before rebels opposed to president Bashar al-Assad fled and Syrian troops moved in. ...