Port the power spectrum calculation code from the FLAMINGO fork

AUTHORS

README

README.md

doc/RTD/source/CommandLineOptions/index.rst

doc/RTD/source/ParameterFiles/output_selection.rst

doc/RTD/source/ParameterFiles/parameter_description.rst

examples/SmallCosmoVolume/SmallCosmoVolume_DM/run.sh

...CosmoVolume/SmallCosmoVolume_DM/small_cosmo_volume_dm.yml

examples/main.c

examples/parameter_example.yml

src/Makefile.am

src/engine.c

src/engine.h

src/engine_config.c

src/engine_io.c

src/periodic.h

src/power_spectrum.c

src/power_spectrum.h

src/random.h

src/row_major_id.h