Finalize v2018.6 release.

SPIRV-Tools v2018.5

Convert validation to use libspriv::Instruction where possible. (Khro…

…nosGroup#1663)

For the instructions which execute after the IdPass check we can provide
the Instruction instead of the spv_parsed_instruction_t. This
Instruction class provides a bit more context (like the source line)
that is not available from spv_parsed_instruction_t.

SPIRV-Tools v2018.4

Support SPV_KHR_8bit_storage

This was used to develop Vulkan CTS tests for VK_KHR_8bit_storage.

SPIRV-Tools v2018.3

Start v2018.4-dev

SPIRV-Tools v2018.2

SPIRV-Tools v2018.1

SPIRV-Tools v2018.0