juliasilge/tidytext: tidytext 0.2.1

Fix bug in augment() function for stm topic model. Warn when tf-idf is negative, thanks to @EmilHvitfeldt (#112). Switch from importing broom to importing generics, for lighter dependencies (#133). Add functions for reordering factors (such as for ggplot2 bar plots) thanks to @tmastny (#110). Update to tibble() where appropriate, thanks to @luisdza (#136). Clarify documentation about impact of lowercase conversion on URLs (#139). Change how sentiment lexicons are accessed from package (remove NRC lexicon entirely, access AFINN and Loughran lexicons via textdata package so they are no longer included in this package)