PDB ligand XML files are replaced by CIF

[jamesmkrieger]

The function fetchPDBLigands now does not work as a consequence:

IOErrorTraceback (most recent call last)
<ipython-input-2-65da2e637be2> in <module>()
----> 1 ligand_data = fetchPDBLigand('STI')

/home/exx/ProDy-website/ProDy/prody/compounds/pdbligands.pyc in fetchPDBLigand(cci, filename)
     95             except IOError:
     96                 raise IOError('XML file for ligand {0} is not found online'
---> 97                               .format(cci))
     98             else:
     99                 xml = inp.read()

IOError: XML file for ligand STI is not found online