Improve font API to use a texture atlas internally.

[Shaptic]

Currently, the font API uses individual quads for every character, and thus causes a performance hit with the excessive state changes when rendering to a obj::CEntity instance.

The suggested model would use a texture atlas internally, thus speeding up rendering performance significantly. All changes should happen behind the scenes, so any documentation should properly transfer to the new functionality and the user should not see any changes in the way they use the API.

• Write texture coordinate offset shader
• Write new font API
• Ensure compatibility with old API calls