Added rect draw api

Added some new maths types
Updated shaders to use new D_Rect structure
Added rect buffers to frames
Misc cleanup

code/vulkan/core.h

@@ -96,6 +96,8 @@ struct Vk_Frame {
 	U32 next_scratch;
 	Vk_CommandBuffer scratch[VK_NUM_SCRATCH];
 
+	Vk_Buffer rbo;
+
 	U32 image; // swapchain image index
 };