By Heekyong Yang and Joori Roh SEOUL (Reuters) -North Korea fired 100 more artillery shells off its west coast on Wednesday, South Korea’s military said, just hours after it launched hundreds of shells into the sea off its east and west coasts in what it called a grave warning to South Korea. North Korea has been carrying out weapons tests at an unprecedented pace this year, firing a short-range ballistic missile and hundreds of artillery rounds near the heavily armed inter-Korean border on Friday. On Monday, South Korean troops kicked off their annual Hoguk defence drills designed to boost th…