add option for alphanumerical prediction symbol WIP

[victorbadila]

My fix for this issue that was least invasive. Check the additional tests in /GaussianNB, it now supports a lot of chars, numbers, etc. as prediction symbols, not only consecutive positive integers. I hat to change what separateClasses returns though and because of this the tests for /MultinomialNB and the rest fail, I haven't updated that part of the code.

Someone maintaining this repo please let me know if they are OK with this direction so far so that I can update the rest of the code and make the rest of the tests pass