module for reading and writing directed graphs

 Graph::ReadWrite is a collection of perl classes for reading and writing
 directed graphs in a variety of file formats. The graphs are represented in
 Perl using Jarkko Hietaniemi's Graph classes.
 .
 There are two base classes, Graph::Reader which is the Base class for classes
 which read a graph file and create an instance of the Graph class, and
 Graph::Writer which is the Base class for classes which take an instance of
 the Graph class and write it out in a specific file format.
 .
 Supported formats: XML, Dot, VCG, daVinci, HTK