Many thanks to Peter and Darian for clearing up my misunderstanding of
how vkResetCommandPool works. The manager creates command buffers from
the command pool on an as-needed basis (when the queue of available
buffers is empty), and keeps track of those buffers in a queue. When the
pool is reset, the queues (one each for primary and secondary command
buffers) are reset such that the tracked buffers are available again.
This allows the array in which the command buffers are allocated to be
allocated on the stack using alloca and thus remove the need to
malloc/free of relatively small chunks.
The scrap texture did very good things for the glsl renderer and the
better control over data copying might help it do even better things for
vulkan, especially with lots of little icons.
It turned out I needed access to the physical device from a buffer
object, so rather than storing the vulkan logical device directly in
buffer (and other) objects, store the qfv logical device.
