Fix scoping error of callback in a for loop
Flesh out the rendering triggering system, so that render requests are propagated up to the scene and trigger a serenader.

This now works and automatically changes the text/color and rerenders the result:

tt = TextTexture(string="Does this work?", color='white')
geometry = SphereGeometry(radius=2, radialSegments=100)
material = LambertMaterial(color='green', map=tt)
myobject = Mesh(geometry=geometry, material=material)

c = PerspectiveCamera(position=[0,10,10], fov=40, children=[DirectionalLight(color=0xffffff, position=[3,5,1], intensity=0.5)])
scene = Scene(children=[myobject, AmbientLight(color=0x777777)])

renderer = Renderer(camera=c, scene = scene, controls=OrbitControls(controlling=c))
show(renderer)
import time
time.sleep(4)
tt.string='hello, how are you'
material.color='yellow'