Copper isn't really useful for anything. Gold tools are almost always a waste of resources. So now, you can craft gold tools and armor from copper. Intended to provide some better tools early game at the expense of always needing copper.

Changes:

Golden tools and armor can be crafted from copper ingots.
Golden tools and armor can be smelted back into one copper ingot.
Recipes for golden tools and armor unlocked by having a copper ingot in inventory.
Gold can no longer be used to make golden tools/armor.

Don't forget that the golden pickaxe can't mine copper or iron ore.