Can't copy or deepcopy a Beam

[ttshimiz]

When using copy.copy(Beam) or copy.deepcopy(Beam) the returned object loses all of its attributes such as Beam.major and Beam.minor.
Sample code:

from radio_beam import Beam
import astropy.units as u

beam = Beam(major=2*u.arcsec)
beam2 = copy.copy(beam)

I think the fix is fairly simple by defining a new __copy__ and __deepcopy__ method for the Beam class.

[keflavich]

This is probably because Beam is a Quantity object and there's something related to numpy array copying that requires a __new__ method, or something like that.