Yeah, been there, done that. Some of the experts might have some really good ideas for you. But when I did this I used one of those putty knives with a chisel edge on it and a hammer to get most of it up with. Then I mixed up some wallpaper remover and dipped rags in it and laid them over the building paper and let them soak while I was removing more tile. It really worked!! It was kind of slow, but it softened things up so I could scrape them off. By the way--hope you're going to put down cement board before you lay your ceramic.