This makes it easily switchable at any point in time.
Still not sure how to properly manage log verbosity cvars:
- cvars are loaded after initialization and map load, so we can't really
depend on saved cvar values.
- reloading cvars each frame cancels `-vkverboselogs` arg that is
supposed to work around the above limitation
Now:
- Not necessarily vulkan-specific cvars are prefixed with `r_`
- Vulkan-specific but not RT-specific things are `vk_`
- RT-specific are `rt_`
Fixes#632
use bits to enable particular performance data display:
0 -- off
1 -- simple frame time
2 -- more object count and sizes statistics (TODO)
4 -- overall gpu usage (TODO)
8 -- extended intra-frame data, function times graph, etc
Ivan Avdeev