df vs. dt

[liza-wood]

This is me talking through my df vs. dt issues. In the process I may have solved it but just curious your thoughts
https://github.com/govscienceuseR/citationExtract/blob/master/dt_df.R

[tylerandrewscott]

Did we make a decision about this? DT is faster, but we can deal with DF if you'd like.