[Lazarus] TAChart DataPointCrossHairTool

[Werner Pamler]

>> Hi, I'm playing with the DataPointCrossHairTool, and I would like to
>> know if it's possible to display the horizontal line on cursor's
>> position, instead as the default data point value.

Not 100% sure, but I believe that this tool always snaps to the data points.
An alternative would be to add a constant line series to the chart and use
a TDatapointDragTool to drag the line. Use the chart's MouseDown to show and
the MouseUp to hide the line. The "toolsdemo" in TAChart's demo folder is an
example of the basic idea (the green and purple dashed vertical lines).