…ommodities. (simonmichael#1563)
The basic goal of this change is to provide more predictable and
intuitive behaviour when using -S/--sort-amount with multiple
commodities. This is achieved by implementing a custom Ord (and Eq)
instance for MixedAmount rather than relying on the derived ones. As a
consequence, all the ways of representing zero with a MixedAmount ([],
[A 0], [A 0, B 0, ...]) are now Eq-ual (==), whereas before they were
not. We have not been able to find anything broken by this change.