Support SPIR-V 1.3 and Vulkan 1.1

The default target is SPIR-V 1.3.

For example, spirv-as will generate a SPIR-V 1.3 binary by default.
Use command line option "--target-env spv1.0" if you want to make a SPIR-V
1.0 binary or validate against SPIR-V 1.0 rules.

Example:
        # Generate a SPIR-V 1.0 binary instead of SPIR-V 1.3
	spirv-as --target-env spv1.0 a.spvasm -o a.spv
	spirv-as --target-env vulkan1.0 a.spvasm -o a.spv

        # Validate as SPIR-V 1.0.
	spirv-val --target-env spv1.0 a.spv
        # Validate as Vulkan 1.0
	spirv-val --target-env vulkan1.0 a.spv