#134 Parse version_id and version_date in parse_xml_web()

[nils-herrmann]

Here is an example:

xml_20029612 = parse_xml_web('20029612')

The resulting dictionary:

{'title': 'Top-hits for H1N1pdm Identified by Virtual Screening Using Ensemble-based Docking.',
 ...
 'version_id': '4',
 'version_date': '2011/01/03',
  ...}

[Michael-E-Rose]

Please update the docstring, then we're good.