big progress

nifty4/library/nonlinear_power_energy.py

nifty4/library/wiener_filter_curvature.py

nifty4/operators/diagonal_operator.py

nifty4/operators/endomorphic_operator.py

nifty4/operators/inverse_operator.py

nifty4/operators/inversion_enabler.py

nifty4/operators/sandwich_operator.py

nifty4/operators/sum_operator.py

nifty4/probing/utils.py

test/test_energies/test_noise.py