Dots per inch chunk

ILBM DPI chunk
==============

Registered by:

Spencer Shanson
16 Genesta Rd
Plumstead
London SE18 3ES
ENGLAND

1-16-90

ILBM.DPI   Dots Per Inch   to allow output of an image at the
same resolution it was scanned at

typedef struct {
	UWORD dpi_x;
	UWORD dpi_y;
	} DPIHeader ;

For example, an image scanned at horizontal resolution of
240dpi and vertical resolution of 300dpi would be saved as:

44504920 00000004 00F0 012C
D P I    size     dpi_x dpi_y

