Help for CROSSHAIR

Simple program to plot a crosshair at the given location on a VICAR file.

The size of the crosshair is given by HEIGHT - that's the size of the
hairs on each side.

The color is specified by DN.  If there are more bands than DNs, the last
DN is repeated.

The file is modified in place.  As such, it must be a pure VICAR file - NOT
a VICAR/ODL dual label.  If you wish to crosshair one of those, use VICAR
copy to create a pure VICAR file, do the crosshairs, and then re-transcode
it if needed.

HISTORY:
2020-01-30 rgd	Initial version
Cognizant programmer: Bob Deen

PARAMETERS: