set axis limits (x or y) of a `ggplot` object (left hand side of `+`) based on the x (`xlim2`) or y (`ylim2`) limits of another `ggplot` object (right hand side of `+`). This is useful for using `cowplot` or `patchwork` to align `ggplot` objects.
xlim2(gg, limits = NULL)
ylim2(gg, limits = NULL)
ggplot2 object with new limits