Reformat CO2 code

[Zachary-Kramer]

There is inconsistent tabbing and spacing in many of the C files, as I had to switch editors half-way through developing and didn't realize the settings were different, and the existing code also had inconsistent sections. Before soilwat_co2_effects is merged, tabbing and spacing should be made consistent. Additionally, we should standardize on using either the Stomatal or WUE term, as using both is confusing. Lastly, shortened names should consistently be used (e.g. use_bio_mult and co2_biomass_mult should be changed).