Customizable U-Hook with improvements

This OpenSCAD-script introduces extra boolean-like parameter for the main hook bottom part:
``light = [0, 1]``
If `light = 0`, the script generates same bottom as the original one.
If `light = 1`, the script generate simplified bottom (as shown on the sample STL), which can be used for lightweight hooks (f.i., hanging towels as in my case).