Added the ratio of TBox:ABox:RBox as a metric.

I've added a new metric.

I'm guessing from the existence of the -h command line option that you run ontometrics over a number of files and then parse the output.  If so, adding this new metric will break your calling tool as the metric is added in the middle of the current output string.

Would you mind if I changed the output format to be a string in JSON format?  Then "higher-level" tools could parse the JSON and we can add new metrics as is fitting.