Python 2/3 compatibility boilerplate

nifty5/dobj.py

nifty5/domains/dof_space.py

nifty5/domains/domain.py

nifty5/domains/gl_space.py

nifty5/domains/hp_space.py

nifty5/domains/lm_space.py

nifty5/domains/power_space.py

nifty5/domains/structured_domain.py

nifty5/energies/hamiltonian.py

nifty5/extra/operator_tests.py

nifty5/library/amplitude_model.py

nifty5/library/apply_data.py

nifty5/library/bernoulli_energy.py

nifty5/library/correlated_fields.py

nifty5/library/gaussian_energy.py

nifty5/library/los_response.py

nifty5/library/point_sources.py

nifty5/library/poissonian_energy.py

nifty5/library/wiener_filter_curvature.py

nifty5/library/wiener_filter_energy.py