Missing implementations on references

[lemmih]

All the implementations for &NotNan are missing. Without an implementation for, say, &NotNan<T> - &NotNan<T>, these types cannot be used as drop-in replacements for f64 and f32. Ideally NotNan and OrderedFloat would implement exactly the same traits as f64 and f32.

[mbrubeck]

#82 implements the std::ops traits on reference types. Example:

fn not_nan<T: Float>(x: T) -> NotNan<T> { NotNan::new(x).unwrap() }

assert_eq!(not_nan(0.0) + not_nan(0.0), 0.0);
assert_eq!(not_nan(0.0) + &not_nan(0.0), 0.0);
assert_eq!(&not_nan(0.0) + not_nan(0.0), 0.0);
assert_eq!(&not_nan(0.0) + &not_nan(0.0), 0.0);

assert_eq!(not_nan(0.0) + 0.0, 0.0);
assert_eq!(not_nan(0.0) + &0.0, 0.0);
assert_eq!(&not_nan(0.0) + 0.0, 0.0);
assert_eq!(&not_nan(0.0) + &0.0, 0.0);

assert_eq!(OrderedFloat(0.0) + OrderedFloat(0.0), 0.0);
assert_eq!(OrderedFloat(0.0) + &OrderedFloat(0.0), 0.0);
assert_eq!(&OrderedFloat(0.0) + OrderedFloat(0.0), 0.0);
assert_eq!(&OrderedFloat(0.0) + &OrderedFloat(0.0), 0.0);

assert_eq!(OrderedFloat(0.0) + 0.0, 0.0);
assert_eq!(OrderedFloat(0.0) + &0.0, 0.0);
assert_eq!(&OrderedFloat(0.0) + 0.0, 0.0);
assert_eq!(&OrderedFloat(0.0) + &0.0, 0.0);

Let me know if I missed anything!

[lemmih]

Thanks!