It's unfortunate that this has the danger of someone writing `impl ToStr for T {}` by accident and then being confused when their stringification crashes the program. I think there was discussion of using attributes to flag at least one of the methods in the trait as being required, but I'm not sure that went anywhere. I don't think that either of these is a good candidate for being blank by default because `to_str` is natural, but slow, and `to_str_writer` is efficient, but doesn't quite make sense initially.

On the other hand, I think that having this method is awesome! This may not be something that should block this initially, but others might have opinions on this as well.