Update atom enthalpies for H, C, N, O, F, Cl, Br, I with data from ATcT

[cgrambow]

I'm going to get this PR going. I used updated data from ATcT. Some things I noticed:

• The previous data for Br was horribly wrong. New data should be double-checked.
• ATcT do not have S data. Where do we get this from? I double-checked that S corresponds to the data in NIST-JANAF.
• Are there new sources for the other atoms/elements?

@dranasinghe, I assigned you to this PR. None of the existing BACs have been corrected yet based on the updated data.

Let's discuss.

RMG-Py PR: ReactionMechanismGenerator/RMG-Py#1955