usage: get_list <base_url> <base_file> <num_list>

    This routine grabs pages from sequential sets of URLs
    and saves them to disk.

    <base_url> is the url to grab from.
    <base_file> is the filename to store that which is
        pointed at by <base_url>.
    <num_list> is a list of numbers and number sequences
        to be plugged into <base_url> and <base_file>.

    <base_url> and <base_file> should each include one printf
    style escape code ('%' followed by options and a type).
    Since only integers will be passed in, probably one of
    the integer types like %d or with modifiers like %03d. will iterate over each number represented by
    <num_list> and use that to format <base_url> and
    <base_file>.  <num_list> is a comma separated list of
    integers and integer sequences with no spaces included.
    An integer sequence is two integers separated by a hyphen.

    Let's say we want to get:
    and save them as do_img02.jpg, do_img05.jpg, do_img06.jpg,
    do_img07.jpg, do_img12.jpg, do_img13.jpg, do_img14.jpg,
    do_img15.jpg, do_img16.jpg, and do_img20.jpg.

    We could use the command:
        get_list '' 'do_img%02d.jpg' 2,5-7,12-16,20