This program takes a multi-image GIF file and generates a single GIF
consisting of all the images overlayed. Each image's screen position
is used. Thus, you can use this together with gifpos and gifasm to
paste together images.
gifovly [-s TransparentColor] [-h]
The GIF to be operated is read in from stdin. The result GIF is written to
Proportional to the size of the input file.
If this index is given, any pixel in images after the first that
has this value is not copied.
Print one line of command line help, similar to Usage above..