Text rendering with Harfbuzz

Here is the first take at Harfbuzz rendering with FreeType. I think the arabic may still be wrong but it's a pretty solid start. I am referencing the Harfbuzz library from my own repository so feel free to move that over to native-toolkit.

![Text Rendering with Harfbuzz](https://cloud.githubusercontent.com/assets/620357/3798735/a582a5f8-1be7-11e4-964e-9912c9fa0c86.png)