Add Sound.copy(), Sound.__copy__(), Sound.__bytes__ methods

[bigwhoopgames]

Was working with sounds and sndarrays recently and noticed Sound didn't have a copy method.

I saw the other issue for implementing Color.copy() and figured why not create one for Sound as well.

bytes might already be implemented but if it isn't it should just do what Sound.get_raw() does already. I didn't test it.

[oddbookworm]

Sound.get_raw() and bytes(Sound) do the same thing already, but a docs improvement is in the cards methinks