images_to_pdf.py needs easier generation of multiple pdfs

[justinliuyuwang]

To improve ease of use, consider adding one of the following:

• python parsing of tsv files containing columns for output filename, each input filename, and basedir - STRONGLY PREFERRED
• a bash wrapper that accomplishes the above
• require standardized inputs (e.g. images named numerically, inside a standardized path within a subject directory: 1.jpg, 2.jpg, 3.jpg... etc)