hadley/ggplot2 — pull request #393 by wch (2012-02-08 08:42:54+00:00)
Title: Control over which sides rugs appear on

I added the ability to control which sides geom_rug appears on. This lets you set it to any of "trbl" for top, right, bottom, and left. Common use cases might include:

* rugs on the top and right, instead of bottom and left.
* rugs on all four sides.
* a rug on just one axis

Some examples from the docs:

```R
p <- ggplot(mtcars, aes(x=wt, y=mpg))
p + geom_point() + geom_rug() # Default: bottom and left
p + geom_point() + geom_rug(sides="b") # On bottom only
p + geom_point() + geom_rug(sides="trbl") # All four sides
```

Let me know if you think there is a better way of doing the `sides` parameter, or if there's a cleaner way to implement it.