Make Money implement Copy

[robinkrahl]

Money has two fields, a rust_decimal::Decimal instance and a reference. Both implement Copy, so Money should be able to derive Copy. The Copy documentation recommends that ‘[g]enerally speaking, if your type can implement Copy, it should.’ What do you think about making Money implement Copy? This would make calculations much less awkward.

[brokenthorn]

Yes, this would fix having to .clone() money instances in cases where you need to calculate various values based off of a common value.

[FirelightFlagboy]

This issue was fixed by #82