multiplot: Multiple plot function
In bi-sdal/sdalr: Convenience functions for the Social and Decision Analytics Lab

This function is taken from the R Graphics Coookbook by Winston Chang. It lays out multiple ggplot objects into a single figure.

1	multiplot(..., plotlist = NULL, file, cols = 1, layout = NULL)

`...`	ggplot objects
`plotlist`	if individual ggplot objects are not passed into `...`, then a `list` of ggplot objects can also be passed
`file`	file?
`cols`	number of columns used to layout the plots, defaults to `1`
`layout`	a matrix specifying the layout. If present, 'cols' is ignored. If the layout is something like matrix(c(1,2,3,3), nrow=2, byrow=TRUE), then plot 1 will go in the upper left, 2 will go in the upper right, and 3 will go all the way across the bottom.