Adjust CLI parameters

[jihchi]

Currently we have following CLI parameters:

Usage: dify [options]

Options:
    -h, --help          print this help menu
    -v, --version       print the version
    -d, --dont-check-dimensions
                        don't check image dimensions
    -b, --diff-based-on-left
                        draw the diff image based on the left image
    -a, --detect-anti-aliased
                        detect anti-aliased pixels. default: false
    -l, --left FILE     the file path of the left image (original)
    -r, --right FILE    the file path of the right image (comparing)
    -o, --output FILE   the file path of diff image (output), output PNG only.
                        default: diff.png
    -t, --threshold NUM matching threshold, ranges from 0 to 1, less more
                        precise. default: 0.1

Minimum usage could be:

dify -l img-base.jpg -r img-check.jpg

Few things on my mind:

1. Get rid of -l, --left FILE and -r, --right FILE, it'd look like dify img-base.jpg image-check.jpg
2. Learning from yahoo/blink-diff, instead of -b, --diff-based-on-left, accepts --copyImageA and --copyImageB otherwise --no-copy (diff mask only)