Finalized warcNgrams/warcNgrams.pig to accept CLI options --minlength, --maxlength, and --stopwords to only keep ngrams in which all words are at least minlength, and at most maxlength long. If the --stopwords switch is provided then only ngrams in which none of the words are stopwords will be retained. The arity of the computed ngrams may now be betwee one and five.