Modelise Beer Lambert absorption for fog
Remove bubble shaders
Factorize some code
Remove a shader callback
Clean some useless decl
Use f0 in fresnel schlick
Use color for specular
Improve smooth camera movement and move settings to user config
Implement sun as an disk area light.

Solid angle is defaulted to sun's one.
Revert "Use color for specular"

This reverts commit fcba1dab86eb785ae366fef338ef31062f6f9540.
Revert "Use f0 in fresnel schlick"

This reverts commit acdafc5566c21abf955485805d4c7c90094f71a6.
Fix sun area light
Tweak variable names
Merge branch 'fpsCam'
Use old formula for glossmap
Fix first player in kart selection doesn't get focused
Merge branch 'upstream/master' into fixes
Change variable names again