Fix the solar metallicity to use Asplund 2009/Grevasse 2010 values
throughout.

Also fix the units in the single-species derived metallicity to account
for the fact that Asplund metallicities are in number density rather
than mass density
Tidy up the various solar abundances
Plot tweaks
Make savefile default to the snapshot directory
Adjust boundaries of ionisation correction plot
 Minor plot tweaks
Remove not needed error ignore
Makefile fix