Sync, threading, and format fixes.

Merge pull request #166 from billhollings/master

vkGetPhysicalDeviceImageFormatProperties returns VK_ERROR_FORMAT_NOT_SUPPORTED.

Allow queue processing to be optionally handled on the submitting (render) thread.

Merge pull request #159 from billhollings/master

Allow queue processing to be optionally handled on the submitting (re…

Add features to support Vulkan CTS and update to latest SPIRV-Cross.

Merge pull request #149 from billhollings/master

Add features to support Vulkan CTS.

Vulkan SDK v1.1.73.0

This is the MoltenVK version that appears in the LunarG Vulkan SDK v1.1.73.0.

Add pipeline caching and reorganize external dependencies.

Merge pull request #120 from hanton/master

Fix typo in Demos/README.md

Updated repository build process.

Merge pull request #108 from billhollings/master

SPIRV entry points, streamline integration with V-LVL & v1.0.1.