Implement cosmo

Implement the cosmology for the interpolation. The details of the computations are in the paper.

src/Makefile.am

@@ -79,11 +79,12 @@ endif
 # List required headers
 include_HEADERS = csds_header.h csds_loader_io.h csds_particle.h csds_time.h csds_tools.h
 include_HEADERS +=  csds_reader.h csds_logfile.h csds_index.h quick_sort.h csds_python_tools.h
-include_HEADERS += csds_interpolation.h csds_parameters.h
+include_HEADERS += csds_interpolation.h csds_parameters.h csds_cosmology.h
 
 # Common source files
 AM_SOURCES = csds_header.c csds_loader_io.c csds_particle.c csds_time.c csds_tools.c csds_reader.c
 AM_SOURCES += csds_logfile.c csds_index.c quick_sort.c csds_parameters.c csds_reader_generate_index.c
+AM_SOURCES += csds_cosmology.c
 AM_SOURCES += $(GRAVITY_SRC) $(STARS_SRC) $(HYDRO_SRC) $(CHEMISTRY_SRC) $(STAR_FORMATION_SRC)
 
 if HAVEPYTHON