juliasilge/tidytext: tidytext 0.1.7

unnest_tokens can now unnest a data frame with a list column (which formerly threw the error unnest_tokens expects all columns of input to be atomic vectors (not lists)). The unnested result repeats the objects within each list. (It's still not possible when collapse = TRUE, in which tokens can span multiple lines). Add get_tidy_stopwords() to obtain stopword lexicons in multiple languages in a tidy format. Add a dataset nma_words of negators, modals, and adverbs that affect sentiment analysis (#55). Updated various vignettes/docs/tests so package can build on R-oldrel