merge from master

.gitignore

demos/__init__.py

demos/critical_filtering.py

demos/wiener_filter_advanced.py

demos/wiener_filter_easy.py

demos/wiener_filter_hamiltonian.py

demos/wiener_filter_harmonic.py

demos/wiener_filter_unit.py

nifty/__init__.py

nifty/field.py

nifty/library/__init__.py

nifty/library/critical_filter/__init__.py

nifty/library/critical_filter/critical_power_curvature.py

nifty/library/critical_filter/critical_power_energy.py

nifty/library/wiener_filter/__init__.py

nifty/library/wiener_filter/wiener_filter_curvature.py

nifty/library/wiener_filter/wiener_filter_energy.py

nifty/minimization/descent_minimizer.py

nifty/minimization/line_searching/line_search.py

...y/minimization/line_searching/line_search_strong_wolfe.py