v0.12.0 - Imgui 0.6.0 and SRGB

Added

• A changelog!
• Shaders are now SRGB aware. Choose RendererConfig::new() to get shaders outputting in linear color
  and RendererConfig::new_srgb() for shaders outputting SRGB.

Updated

• imgui to 0.6.
• winit to 0.23

Removed

• GLSL shaders and glsl-to-spirv. If you want a custom shader, provide custom spirv to RendererConfig::with_shaders(), however you generate it.