add a `dashStyle` that can show the direction the line is going
When showing a line on scatter chart it can be hard to tell where the line started and where it ended.
Having a dashStyle option that was similar to plotOptions.scatter.dashStyle = 'dot' except that instead of a dot it was a rotated triangle that pointed in the direction the line was going would be awesome.
I saw some hacks for turning the entire line into one long arrow but that isn't what I was looking for.
A possible way to do it is to use SVG markers, see http://jsfiddle.net/4qgy4rmh/1/.