STRUCTURE: UF_CGM_custom_widths_t

DESCRIPTION: This structure describes a width palette. It can be used to
map the line widths of a display image when creating a CGM.

It gives the units in which all the widths are stored, single width information,
the custom width definitions, and an entry for each color.

The 'use' member specifies the primary selection of which
type of width assignment to use.

The 'single_width' member contains the last-typed value for
the user-defined width to use when UF_CGM_width_user is
selected for member 'single'. It is always defined, even when
'single' is not set to UF_CGM_width_user.

The 'single_source' member contains a value when the 'single'
member is UF_CGM_width_std or UF_CGM_width_custom. The value
is the index in the 'custom' width array or the standard width
index value. Both are assumed to be in internal order, normal,
thick, and thin for 0, 1, and 2, respectively.

Note that 'single_source' is undefined when 'single' is
UF_CGM_width_single.

The 'widths' array is indexed by the color index straight
out of the database, or 1-216. Therefore the array is one
longer than the actual number of colors, or 217.

Note: the structure has been devised to be amenable to
increasing the number of width indices.