Improve graphics API to reduce return values

[asarium]

This is an effort to clean up the graphics API a bit and reduce return values that are not really needed.

The reason behind this is to reduce the amount of synchronization points necessary when implementing a threaded rendering backend. The easy way to do threading is to just dispatch graphics calls to a separate thread. However, if there are return values involved, there needs to be synchronizations which defeats the point of multi-threading.