Added the Zero and One traits to sigils.

It looks like these may be removed from the standard library soon.

src/integer.rs

@@ -22,7 +22,7 @@ use super::number::Number;
 /// [10]: https://doc.rust-lang.org/std/primitive.i64.html
 /// [11]: https://doc.rust-lang.org/std/primitive.isize.html
 /// [12]: https://doc.rust-lang.org/std/index.html
-pub trait Integer : Number
+pub trait Integer: Number
 {
 }