Felix SalmonPhoto illustration: Annelise Capossela/Axios. Photo: Jamie McCarthy/Getty ImagesAt some point in the next few years, a charitable trust will be created that will immediately be the largest such entity in the world. Amazingly, no one seems to have given much thought to what it might do or where it will spend its money.Why it matters: Warren Buffett's yet-to-be-named charitable trust will be 100% effective from day one at ensuring that his estate pays no tax on the billions he has made...