Properly implement Base.hash() for custom type

General Usage
2

I don’t think there’s any reason to supply a default for the second argument (the base hash(x::Any) method in Base will do this for you). And you can probably simplify the implementation a bit to something more like:

function hash(weapon::GameWeapon, h::UInt)
  hash(weapon.type, hash(weapon.damage, h))
end