Merge branch 'NIFTy_5' into adjust_variances

Dockerfile

README.md

demos/bench_gridder.py

demos/getting_started_1.py

docs/source/code.rst

docs/source/installation.rst

docs/source/volume.rst

nifty5/__init__.py

nifty5/data_objects/numpy_do.py

nifty5/extra.py

nifty5/library/gridder.py

nifty5/library/smooth_linear_amplitude.py

nifty5/operators/convolution_operators.py

nifty5/operators/energy_operators.py

nifty5/operators/harmonic_operators.py

nifty5/operators/operator.py

nifty5/operators/scaling_operator.py

nifty5/sugar.py

test/test_operators/test_adjoint.py

test/test_operators/test_nft.py