#579 Vertical error bars in key

[oruxl]

I haven't found a way to change the direction of the error bars drawn in Gnuplot's key from horizontal to vertical. I think this feature is important because, e.g., it is confusing to have a key which shows horizontal error bars when only vertical error bars are present in a figure.

The accepted answer from a web search is this: https://stackoverflow.com/questions/30218955/gnuplot-legend-errorbar-symbol-vertical, which suggests a hack to manually draw the key using arrows and labels. This solution prevents using the many nice options already implemented for keys.

Attached image shows an example plot with yerrorbar and set key, but the key draws only horizontal error bars.