Macro visit_diff::assert_eq_diff

macro_rules! assert_eq_diff {
    ($left:expr, $right:expr) => { ... };
    ($left:expr, $right:expr,) => { ... };
    ($left:expr, $right:expr, $($arg:tt)+) => { ... };
}

Replacement for the standard assert_eq! macro that prints a debug_diff between its arguments on failure.