Update axis/legend labels
Examples
p <- ggplot(mtcars, aes(mpg, wt)) + geom_point()
update_labels(p, list(x = "New x"))
update_labels(p, list(x = expression(x / y ^ 2)))
update_labels(p, list(x = "New x", y = "New Y"))
update_labels(p, list(colour = "Fail silently"))