Add support for multiple light sources

[R366Y]

Change World struct

   mutable struct World{T<:GeometricObject}
    objects::Array{T,1}
    light::Array{PointLight,1}

Change function shade_hit(..)

    for light in world.lights 
    shadowed = is_shadowed(world, comps.over_point)
    surface = lighting(
        comps.gobject.material,
        comps.gobject,
        world.light,
        comps.over_point,
        comps.eyev,
        comps.normalv,
        shadowed,
    )
    end

[R366Y]

Merged into master 2b3ec42