Add, to metadata of any PDF, name of the R file that creates the figure

[jbullock35]

This new feature would be written into latexTablePDF.R. Something like "Created by XXX.R" would appear in the PDF metadata.

This improvement would require two steps:

1. Find the R filename. Probably possible only if using Rscript or Rstudio. See https://stackoverflow.com/questions/1815606/determine-path-of-the-executing-script and https://stackoverflow.com/questions/18264683/how-to-get-the-file-name-of-the-r-script-currently-being-executed-for-easy-auto.
   • Or I can just explicitly store the filename as a string. This is a second-best option but still better than nothing.

2. Add the filename to the metadata. pdfcrop doesn't seem to have this ability, so I would need to use some other tool. https://rdrr.io/github/skgrange/threadr/man/pdf_write_metadata.html is promising. It relies on exiftool; see https://stackoverflow.com/questions/18647777/. If that doesn't work, consider pdftk.
   • The pdftools package won't help. It reads PDF files but doesn't write to them.