Ported ngramrr here. Remove ngramrr dependency, add tau to DESCRIPTION

[chainsawriot]

Hello. I am the author of ngramrr. I have a plan to remove ngramrr from CRAN because there are actually better, highly efficient ngram tokenizers out there (e.g. tokenizers). As your package is the only package using ngramrr, I think I shouldn't break your package. As an interim solution, I have ported all functions from ngramrr to your package. But I think in the long run, it would be good for you to use something else, e.g. tokenizers. I will keep ngramrr on CRAN, until you have updated this package on CRAN.

BTW, on my machine, I can't pass one of the unit tests. test.analyzeSentiment.R:80

From my understanding of F1 score, the F1 score for that case (4TP, 0FP, 0TN, 0FN) should be 1, not 0.