This function provides a simple way to modify the panel border in ggplot2. It
doesn't do anything that can't be done just the same with
theme(). However, it
saves some typing.
panel_border(color = "grey85", size = 1, linetype = 1, remove = FALSE, colour)
The color of the border.
Size. Needs to be twice as large as desired outcome when panel clipping is on (the default).