Prevent output to terminal for 1 file w/ N graphs.

[step-]

Issue: when the input file includes multiple graph {...}
GraphvizCompile outputs the first graph to file a:output but all
remaining graphs are sent to the output terminal (gibberish).

This solution: Use dot -O which ignores -o a:output and writes each
graph in a separate, numbered output file. The first graph is output to
input_file_with_ext.output_ext, and GraphvizOutputFile changes
accordingly.

TODO ?? Alter GraphvizInteractve to show the remaining graphs.

[step-]

To change the code as little as possible I opted for setting shelloptions instead of changing the Compile function code block. However, a more robust change should implement option "-O" in the Compile function itself.