Merge pull request #86 from Simmesimme/feature/new_renderer

Feature/new renderer
Pass RenderContext to make_pass.
Use PipelinePass for all passes during runtime.
Remove obsolete constructor.
Simplify process signature.
Store PipelinePass per value.
Use override specifier.
Pass PipelineDescription to process method.
Add some comments.
Apply clang-format.
Use RenderMode::Callback for SSAOPass.
Use RenderMode::Callback for BBoxPass.
Add pass for emissive objects.
Move emissive lighting into separate pass.
Check explicitly for RenderMode::Callback.
Delete unnecessary lines.
Add RenderMode::Quad.
Use RenderMode::Quad.
Copy attributes vom PipelinePassDescription.
Use {blend,depth_stencil,rasterizer}_state_desc.