Text support

[sunjay]

Support drawing text. Similar in function to the Python turtle.write method.

If someone would like to take this on, please leave a comment and I'll provide more detailed implementation steps. Adding text is not going to be super difficult, though it will take some insight into how the library works in order to implement it properly. Text will be implemented as a new kind of drawing primitive, similar to the Line and Polygon primitives we currently support. Pathfinder does support rendering text via the fill_text method, so we can use its APIs to implement this feature.