Per-instanced data was previously stored in uniforms. This required
several OpenGL calls to upload all of the data, and it was more complex
to prepare (several vecs vs one).
Additionally, drawing APIs are now accessible through a `RenderApi`
(obtained through `QuadRenderer::with_api`) which enables some RAII
patterns. Specifically, checks for batch flushing are handled in Drop.
This moves some logic that was previously being done per-character into
the vertex shader. At this time, we've traded CPU computation for
additional gl::Uniform2f calls. This is only a marginal improvement.
However, this patch positions the renderer well for instanced drawing,
and that will be a huge performance win.
Joe Wilm