tm_clean: Clean subject line text prior to analysis
Description
This function processes the Subject column in a Meeting Query by applying
tokenisation usingtidytext::unnest_tokens(), and removing any stopwords
supplied in a data frame (using the argument stopwords). This is a
sub-function that feeds into tm_freq(), tm_cooc(), and tm_wordcloud().
The default is to return a data frame with tokenised counts of words or
ngrams.