By Martyn Herman RIO DE JANEIRO (Reuters) - Australian former world champion track cyclist Melissa Hoskins has called time on her career at the age of 25, saying "there is only so much pain" she can handle. Hoskins had dreamed of going out with a medal in Rio but, from the moment she and her team pursuit squad crashed heavily in training on Monday, the odds on that happening grew. "There is only so much pain you can handle," said Hoskins, who suffered a bout of pneumonia this year. More...