code: def process_forcefield(*forcefields):
      
      for forcefield in forcefields:
          if forcefield.endswith('.frcmod'):
              gaffmol2 = os.path.splitext(forcefield)[0] + '.gaff.mol2'
              yield create_ffxml_file([gaffmol2], [forcefield])
          else:
              yield forcefield
docs: Given a list of filenames, check which ones are `frcmods`. If so,
      convert them to ffxml. Else, just return them.