"Enhance" save multi-method to be able to print to std-out

I found myself with a need to print an incanter dataset to *out*, and it seemed like it would make the save function that much more versatile.

I chose to follow the *nix convention of referring to std-out as "-", because it seemed pretty reasonable.  I think that there is probably a better way to refactor the code to accomplish what I'm after (which is basically to stringify an incanter dataset in csv format) but I couldn't find a function to do this, I apologize if I missed it.