Fix testing for multiple classes

[PSSF23]

My issue is that I cannot implement testing for a dataset that contains more than two classes, even though I can train the model without such a limitation.

I obtained my LIBSVM data from this website and executed the following command:

./bin/spdt --model-path ./tmp --class-labels 0,1,2,3,4,5,6,7,8,9 --training-data pendigits --test-data pendigits.t

And the error I received is as such:

Exception in thread "main" java.lang.IllegalArgumentException: evaluation not implemented for more than two classes!
	at com.soundcloud.spdt.SPDT.eval(SPDT.scala:614)
	at com.soundcloud.spdt.Application$.main(Application.scala:160)
	at com.soundcloud.spdt.Application.main(Application.scala)

Please let me know if I have made any implementation mistakes. Thank you.