Add thermodynamic potentials

Not ready to be merged. Opening for comments/suggestions.
You want *more* accuracy? So picky :P

I'm not sure this will ever make a difference, but I can grab the data from the other standards body (the CIAAW), which is where "google" got its number from. Actually, Al is now even better known - but it's unusual in that it only has one isotope (Al26 is too short lived to be alive except in the proximity of supernovae).

The CIAAW data is in Excel form here: http://www.ciaaw.org/pubs/TSAW2013_xls.xls