MDL molfile/SDF (V2000) reader/writer

 Chemistry::File::MDLMol automatically registers the 'sdf' format with
 Chemistry::Mol.
 .
 The parser returns a list of Chemistry::Mol objects. SDF data can be accessed
 by the $mol->attr method. Attribute names are stored as a hash ref at the
 "sdf/data" attribute, as shown in the synopsis. When a data item has a single
 line in the SDF file, the attribute is stored as a string; when there's more
 than one line, they are stored as an array reference. The rest of the
 information on the line that holds the field name is ignored.