Macro approx::relative_eq

macro_rules! relative_eq {
    ($lhs : expr, $rhs : expr $(, $opt : ident = $val : expr) *) => { ... };
    ($lhs : expr, $rhs : expr $(, $opt : ident = $val : expr) *,) => { ... };
}

Approximate equality using both the absolute difference and relative based comparisons.