As he teetered on a narrow rock ledge a yak's bellow short of the stratosphere with a rubber mask strapped to his face a pair of mittens the size of a sealion's flippers and a drop of two kilometres below him it's fair to say Mark Horrell wasn't entirely happy with the situation he found himself in.He had been an ordinary hiker who had only read books about mountaineering. When he signed up for an organised trek in Nepal with a group of elderly ladies little did he know that ten years later he w