change public header so all names are prefixed VDWXC_ or vdwxc_
Also, VDWXC_DF1 and VDWXC_DF2 are the only two recognized functionals (CX was synonym with DF1 because we only calculate nonlocal part, so basically we cut out the synonyms)
Also, VDWXC_DF1 and VDWXC_DF2 are the only two recognized functionals (CX was synonym with DF1 because we only calculate nonlocal part, so basically we cut out the synonyms)