This last week I was shocked, as I am sure many others were, by Jon Snow's public revelation he has been diagnosed with Alzheimer's. His decision to go public is important and should give others hope. It will also shine a light on the need for more research and more help for all who suffer from any form of dementia. Jon was a chum in the old ITN days.His predecessor as presenter of Channel 4 News, Peter Sissons, had been a closer friend, as we w…