Pass cine-extract's output dir on the command line, and make sure it exists.
Rearranging cine-extract slightly in preparation for other output formats.
removing extraneous whitespace
update comments in .gitignore
updating copyright with respect to changes coming
unifying style for conditionals and loops
updating copyright years in LICENSE
moving extract_to_ppm_dir above main
refactored out ordinal_suffix utility function
ignore generated cine-extract.d
added assertion on outbuf_out
commenting function definitions

(also, changed extract_image_by_frame_id to offset_for_frame_id -
note that this function is currently unused.)