Change frame delay in GIF file

Change the frame duration in a GIF file

USAGE
change_gif_delay(gif_file,frame_dur,output)
change_gif_delay(gif_file,frame_dur,output,overwrite)

INPUT
- GIF_FILE: original GIF file
- FRAME_DUR: frame duration (in seconds)
- OUTPUT: output file name. If the path is not specified, it will be saved in the same folder as GIF_FILE
- OVERWRITE: 1 (overwrite OUTPUT) or 0 (do not overwrite). Default: 0