Compatibility with current pymc3, theano, arviz and python

[moltaire]

GLAMbox currently only runs on Python 3.7. PyMC3 and arviz have made a lot of progress in the meantime.
I think it would make sense to check if we can update GLAMbox without rewriting it.

[YuanboBQ]

Very hope GLAMbox could be compatible with Python 3.8 or 3.9. Thank you so much.