Write generational output

[kirbyherm]

So I have a particular problem where I would like to save ALL the outputs from the evolutionary algorithm I'm using, not just the final population. I have hardcoded a method for implementing this, where I simply save the population at each generation to a csv file.

Adding this PR here mainly to ask if this would be a worthwhile implementation to add across the board (either as an additional parameter, or as an additional public function similar to set_verbosity().

As is, I would not pull this in but was wondering if it was worth developing further.