Backend support implemented in GL, Metal and D3D12.
Support for unorm values in the GL backend requires a
utility function to indicate if the format's components
are normalized.
Note that unorm_r8 is only supported on more recent MacOS SDKs (10.13),
so it's omitted for now.
This directory used to contain both the state tracking code for the
backends, and the common utilities that could be used both by the
backends and the rest of the code. Things are now:
- src/common is utility code for the whole repo
- src/backend contains libNXT's code
- src/utils is utility code that we don't want in libNXT
This commit also changes all includes to use global paths from src/
bacause it had to touch a bunch of #include statements anyway.
