Function to make an index file for output of batch_species()
make_species_index.RdSearches through a directory containing output from batch_species() and
create an index file with columns:
"species", "hdf5", "size", "breeding_quality", "nonbreeding_quality",
"postbreeding_migration_quality", "prebreeding_migration_quality",
"min_quality", "xmin", "xmax", "ymin", "ymax")