Specular color affecting reflections

The RGB values should be premultiplied by the alpha value.

Property definitions

gamnit $ SmoothMaterial :: specular_color
	# Specular color affecting reflections
	#
	# The RGB values should be premultiplied by the alpha value.
	var specular_color: Array[Float] is writable
lib/gamnit/depth/more_materials.nit:45,2--48,45