Return integrals as Numpy arrays rather than tuples

[kimt33]

The integrals of the Hamiltonian, integrate_sd_sd and integrate_wfn_sd, are returned as tuples of one electron integral, coulomb integral, and the exchange integral. It's a bit of a pain to add together these values.

The returned value can either be the sum or the numpy array of the three integrals. I'm not sure exactly when it would useful to have this information, but it might not be a bad idea to keep them separated. Numpy array should make it easier to manipulate these integrals.