Returns a hash that represents the difference between two hashes.
Examples:
{1 => 2}.diff(1 => 2) # => {} {1 => 2}.diff(1 => 3) # => {1 => 2} {}.diff(1 => 2) # => {1 => 2} {1 => 2, 3 => 4}.diff(1 => 2) # => {3 => 4}
[Validate]