`to_string()` vs `to_owned()` for string literals

[oli_obk]

@DroidLogician

This may be fixed in the future with specialization, as str could implement ToString directly instead of having it go through the generic impl<T> ToString for T where T: Display {} implementation, which employs the formatting framework. But currently I do concur with your recommendation.

Now that specialization for str::to_string() has landed, we can safely say that to_string() has the same performance as to_owned(), and thus to_string() should be used since it's more clear