Code cleaning part 2
Functions no longer returning bizarre lists of tuples of lists or things of the like
get_alts() now just returns a list of weights, as the ref_ngram is known at call time and the alternate
will always be equal to ngram
bleu() has some tiny algorithmic changes around the call to get_alts() as a result of this change, resulting
in cleaner and clearer code
Used a more functional strategy in calculating the score from the totals lists, clearer to me and seems to run
a little bit faster, not that that is super important
Finally, general code clean up (moving constants and variables as far up as possible, etc.) and addition
of comments.