Graphviz .dot support

[saxondigital]

Support generating glyphs from Graphviz '.dot' files. This is a natural extension to the gitviz functionality (issue #169.) By reading the dot files we can graph git repos (using the other gitviz projects dot output files,) as well as a variety of other graphs. Please see the link for example data sources:

http://graphviz.org/content/resources

Could use Doxygen (or other tools) to generate the intermediate DOT files for Code Visualization.