long overdue cleanup

demos/polynomial_fit.py

nifty5/library/amplitude_model.py

nifty5/library/correlated_fields.py

nifty5/library/inverse_gamma_model.py

nifty5/library/los_response.py

nifty5/multi_domain.py

nifty5/operators/block_diagonal_operator.py

nifty5/operators/central_zero_padder.py

nifty5/operators/chain_operator.py

nifty5/operators/diagonal_operator.py

nifty5/operators/dof_distributor.py

nifty5/operators/domain_distributor.py

nifty5/operators/endomorphic_operator.py

nifty5/operators/energy_operators.py

nifty5/operators/exp_transform.py

nifty5/operators/field_zero_padder.py

nifty5/operators/harmonic_operators.py

nifty5/operators/inversion_enabler.py

nifty5/operators/laplace_operator.py

nifty5/operators/mask_operator.py