
The Chart class is my favorite baby. It is used
to display a chart defined by a sequence of
pairs (x,y).  The pair is a CL_Pair that is 
derived from the template class Pair.
The base class Pair comes with operators
for comparison, where the x-values are
compared first and the y-values second.
CL_Pair specializes the template types
to double for x and y, and has the interface
that is necessary to be used as a YACL-base
type.  The chart class transforms a given
pair sequence into an array of points that
is used for drawing a polygon.  You actually
can choose between a linear or gradual connection
of the points.  The x-axis and the y-axis are labeled
automatically, where the minumum of x/y is used as
starting point (so insert pair(0,0) if you want to
have this as origin). The formatting of the numbers displayed
at the x/y-axis is done by a StringConverter.
A label is used for the description of the x/y-axis (at the end 
of the line) and the title (that is displayed at the top center).
Therefore we have a VObjCollection as base class.