Ramp Lighting for Godot

Simple ramp lighting with rim light and specular highlighting. Comes with 2 example ramps. Ramp textures must have "Repeat" import parameter set to "Disabled", otherwise they will generate artifacts. Works with GLES2 and performance is generally good. Not sure how good it'd be on mobile, however. Supports shadows. GLES3 version simply adds the diffuse to itself to support multiple lights.