Add Vulkan support

[mogemimi]

Hello guys, I've just started to implement the interface for Vulkan APIs.

Progress

• [x] Buffer
  • [ ] Add SetData()
  • [ ] VertexBuffer
  • [ ] IndexBuffer
  • [ ] ConstantBuffer
• [ ] EffectReflection
• [ ] GraphicsCommandList
• [ ] GraphicsCommandQueue
• [x] GraphicsDevice
  • [x] Enumerate GPUs
  • [x] Create instance and Vulkan device
  • [ ] Add create-graphics-resource functions
• [ ] PipelineState
• [ ] RenderTexture
• [x] SampleState
• [x] Shader
  • [ ] Add SPIR-V compiler
• [x] Texture2D
  • [ ] Add SetData()

Misc

• [ ] Update build settings
• [ ] Add CMake support
• [ ] Update docker image for Ubuntu/Linux game dev
• [ ] Merge feature/metal branch and add Metal support

[mogemimi]

I've cherry-picked it and merged one of their commits into master, please see: https://github.com/mogemimi/pomdog/pull/8