Simple dotted pattern (feature request)

[DanChaltiel]

Hi,

First, thanks for this great package!

I wondered if there was a way to tweak your geoms in order to add "simple" patterns like the dotted one (similar to the dotted texture in MS Excel).

For now, it does not seem possible to use a non-image as a pattern, I tried to tweak it myself but I do not master ggplot prototypes enough yet.

Do you think this is something addable to your package?