Function for creating mosaic plots

Hi to everybody!
In the last few days I've worked on a version of the Mosaic Plot (see <http://www.statmethods.net/advgraphs/mosaic.html>).
It's still quite crude but has a solid base of tested functions and can be modified/extended quite easily to get closer the R version.

here is an example of the results:
![mosaic_plot](https://f.cloud.github.com/assets/1419337/65333/d6b243f2-5e76-11e2-99f3-5c023240079d.png)

It's actually pretty much self contained so should work without any interaction with the rest of the system.

I put it in the sandbox because wasn't sure of the quality standard for being into the main graphical section.