Merge branch 'py3' into develop

README.rst

bfps/__init__.py

bfps/base.py

bfps/code.py

bfps/cpp/fftw_tools.cpp

bfps/cpp/field_descriptor.cpp

bfps/cpp/fluid_solver.cpp

bfps/cpp/fluid_solver_base.cpp

bfps/cpp/slab_field_particles.cpp

bfps/cpp/tracers.cpp

bfps/fluid_converter.py

bfps/fluid_resize.py

done.txt

setup.py

tests/test_convergence.py

tests/test_plain.py

todo.txt

tox_convergence.ini

tox_io.ini

tox_plain.ini