This function is a wrapper for parseKGML and KEGGpathway2Graph. It
takes two actions: first it reads in the KGML file and parses it into an object of
KEGGPathway-class, the second step it calls
KEGGpathway2Graph function to return the graph model.
Note that groups of genes will be split into single genes by calling
the KEGGpathway2Graph function. Edges that connected to
groups will be duplicated to connect each member of the group.