Refactor files to use s2::s2string instead of std::string, right now they are identical.
It is done the benefits of future.
Moved the vertex and index buffer function from GraphicPipeline to VertexShader.
Moved DepthStencil function from GraphicPipeline to PixelShader.
The user should benefit from providing less parameters as the binding information of vertex
input(vertex and index buffer) and pixel output(render target and depth stencil buffer)
could be told from the shader. This also offers better error checking.
Added missing declaration.