Update the max number of particles per input hdf file
Update the max number of particles per input hdf file

The type of the hdf header structure npart has been changed from int to unsigned long int, increasing the maximum number of particles that can be correctly read from an input hdf5 file. 
pelahi/VELOCIraptor-STF,pelahi/VELOCIraptor-STF,pelahi/VELOCIraptor-STF