* This will let us run multiple windows (and multiple threads) relatively
easily.
* The hammer is fairly big, we move some things into the window that don't need
to be there necessarily if we have multiple windows on a single thread, but it
keeps things simple.
* Instead of only doing a very lightweight check to see if the API is available
up-front, we now share the API initialisation among all API tests far enough
to determine availability of extensions, features, etc. Then we can precisely
determine which tests are available and which aren't before running.
* We also fix a number of issues that could cause incorrect formats to be
generated.
* Test cases added for D3D11/GL/Vulkan to test different struct types. These
aren't automated at the moment because most of the code they're testing is in
the UI itself.
baldurk