add a repack function for repacking hdf5 files
by default: use separate hdf5 files for each site and for the sites table so repacks are cheaper timewise
add tests to make sure file sizes don't grow unnecessarily
add autorepack kwarg to update_site_list and update_site_data to control whether
or not the files get automatically repacked
add missing test file
update docstrings for path parameter
write a real docstring for repack()
correctly find last refreshed
handle relative paths (with no dirname)
shortcut updating/repacking if there are no new values
fix empty get_sites check: use normalized sites path