`geom_pointranges()`

[aphalo]

A geom like geom_pointrange() but with range lines for both x and y. This would complement ggpmisc::stat_centroid() allowing centroid plus x and y error bars in a single plot layer. I do not use capped ranges much, but users may also expect to find a geom_errorbars() for x plus y capped error bars.

These geoms should not be too difficult to implement, I think.