GraphicsMagick Draw Functions

I've added bindings for a pretty large subset of the [draw api](http://www.graphicsmagick.org/api/draw.html).

At the moment, I haven't written the path functions, most push/pop operations, and the get part of most of the get/set functions.

Example usage would be something like

```haskell
withDrawContext myImg (drawSetStrokeColor r g b o >=> drawLine 10 10 30 10)
````
And the type of withDrawContext is

```haskell
withDrawContext :: HImage -> (Ptr DrawContext -> IO (Ptr DrawContext)) -> HImage
```