rm. APPEND and
       MARGIN are optional inputs.
 
    <a href="crop.html">CROP</a>('filename.ext') crops the image in the file and saves it using
    the original filename, overwriting the old image. The extension (ext)
    can be anything IMREAD supports.
 
    <a href="crop.html">CROP</a>(directory) crops all images in a directory. 
 
    If APPEND is 1, <a href="crop.html">CROP</a> saves the cropped image as 'filename_crop.ext'
    in the same directory as the original.
 
    MARGIN sets the margin wid