Internal links are linking to the wrong subdirectory.

Internal links between classes in different modules is referencing the module of the current class, not the module of the referenced class.

For example, on [ofImage](http://www.openframeworks.cc/documentation/graphics/ofImage.html), the link to ofTexture goes to http://www.openframeworks.cc/documentation/graphics/ofTexture.html, not http://www.openframeworks.cc/documentation/gl/ofTexture.html.

This pull request fixes the problem—I'm not very familiar with Python, so if there's a more efficient or idiomatic way to do this, please let me know.