No major changes to functionality. Mostly source code formatting changes and one bugfix. The program now has the ability to open a larger number of files because it doesn't try to open all the input images at the same time

- rewrapped to 79 columns
- renamed parser to ARGP
- renamed args to ARGS (uppercase because it's global)
- renamed main() to pdf_from_images()
- changed the images argument type from file to str (because the file type opens all the given image files at once which can cause us to hit the maximum open file limit when we are supplied with more than about 250 image files (e.g. on OSX)
- passing pdf_from_images a "props" dict instead of a bazillion arguments in the prototype. this is better than typing the attribute names:
  - in the argparse add_argument call
  - in the main/pdf_from_images call
  - in the main/pdf_from_images prototype
  - in the main/pdf_from_images function body
- reduced some duplication in the construction of the info dict
- changed the formulation of the result from a bunch of concatenations to list append operations and finally a join
- pep8 compliance changes
- some pylint compliance changes