Merge branch 'feature/rFFTW-distributed-particles' into develop

bfps/cpp/distributed_particles.cpp

bfps/cpp/distributed_particles.hpp

bfps/cpp/interpolator.hpp

bfps/cpp/interpolator_base.hpp

bfps/cpp/particles.cpp

bfps/cpp/particles.hpp

bfps/cpp/particles_base.cpp

bfps/cpp/particles_base.hpp

bfps/cpp/rFFTW_distributed_particles.cpp

bfps/cpp/rFFTW_distributed_particles.hpp

bfps/cpp/rFFTW_interpolator.cpp

bfps/cpp/rFFTW_interpolator.hpp

bfps/tools.py

setup.py

tests/base.py

tests/test_particle_classes.py