Makes the global a member of the RendererBase class. We also change this
to be a reference. Passing any form of null pointer to these functions
is incorrect entirely, especially given the code itself assumes that the
pointer would always be in a valid state.
This also makes it easier to follow the lifecycle of instances being
used, as we explicitly interact the renderer with the rasterizer, rather
than it just operating on a global pointer.
The OpenGL renderer has been revised, with the following changes:
- Initialization and rendering have been refactored to reduce the number of
redundant objects used.
- Framebuffer rotation is now done directly, using texture mapping.
- Vertex coordinates are now given in pixels, and the projection matrix
isn't hardcoded anymore.
