Cannot create Spin hilbert with odd sites and S=1

Created by: PhilipVinc

Reported by @fabienalet

>>> import netket as nk
>>> nk.hilbert.Spin(1.0, N=3, total_sz=1.0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/filippovicentini/Dropbox/Ricerca/Codes/Python/netket/netket/hilbert/spin.py", line 88, in __init__
    _check_total_sz(total_sz, N)
  File "/home/filippovicentini/Dropbox/Ricerca/Codes/Python/netket/netket/hilbert/spin.py", line 40, in _check_total_sz
    raise Exception(
Exception: Cannot fix the total magnetization: Nspins + totalSz must be even.

the cuprit is the second check in here: (size is number of spins)

def _check_total_sz(total_sz, size):
    if total_sz is None:
        return

    m = round(2 * total_sz)
    if np.abs(m) > size:
        raise Exception(
            "Cannot fix the total magnetization: 2|M| cannot " "exceed Nspins."
        )

    if (size + m) % 2 != 0:
        raise Exception(
            "Cannot fix the total magnetization: Nspins + " "totalSz must be even."
        )

The second check works only for Spins 1/2. Can we generalise it to always work? I'm too tired to think how to now.