New functions and features

Clicking on topics highlights all points in that topic, and renders points from non-selected topics as grey with low opacity
New 'processing' tab allows manipulation of arguments passed to make_dtm

Apps that record screening information now do so in a unique column starting with 'selected_', allowing users to determine at which stage articles were excluded during the screening process. New column names are as follows:

All apps now use the same naming convention for selection/exclusion (previously screen_topics returned TRUE/FALSE)
screen_abstracts and screen_titles no longer add 'color' or 'order' columns to exported objects

Now accepts objects of class data.frame as an input
Flexible bigram detection c/o package 'ngram'
Chooses words for display by number of characters, rather than frequency of occurrence in the dataset
Allows user-controlled removal (the default) or retention of empty rows

screen_abstracts automatically moves to the next reference when a selection is made, and hides screened articles by default
read_bibliography now recognises ris tags from Web of Science (.ciw format)
add_line_breaks now available as a standalone function, as well as being an argument in format_citation
objects returned by find_duplicates now include information on the call that created them (via attributes)

Changed defaults

find_duplicates now searches for exact matches of DOIs by default, or fuzzy matching of article titles if DOIs are missing
make_dtm now returns an object of slam::simple_triplet_matrix rather than matrix. This can be coerced to a matrix by as.matrix

merge_columns should return columns in the same order regardless of order that objects are provided
Importing multiple files at once no longer generates non-unique 'label' entries, which could cause failure of article citations in screen_topics.
csv files now import with correct text encoding using read_bibliography
screen_duplicates loads data.frames correctly from the command line
data.frames returned by read_bibliography always have snake case column names
make_dtm now removes all words of three letters or fewer
Improved behaviour of format_citation