By Ian Ransom MELBOURNE (Reuters) – Ash Barty sent shockwaves around the tennis world on Wednesday when she abruptly announced her retirement at the peak of her game and just two months after claiming a third Grand Slam title at the Australian Open. Citing the fulfilment of her tennis goals and fatigue with life on the Tour, the 25-year-old world number one walks away with 15 titles to her name, the last coming at Melbourne Park where she ended Australia’s 44-year wait for a home champion. “I know how much work it takes to bring the best out of yourself … I don’t have that in me anymore,” sh…