#26 Add a graphics API

[Kevin Rogers]

Now we have image loaders and save functions we
could really use the ability to draw on these images.

We should add a 2D graphics API. I would suggest
functions that are very similar to the Java 2D Graphics
API. I'm not sure how far we should go with this support
initially, but I can see the benefit of intially adding the
basic drawing operations and clipping.