Procedures for bending models on the surface of a cylinder or into a parabola in OpenSCAD

This is a continuation of OpenSCAD bend procedures by flavius on Thingiverse, updated for modern versions of OpenSCAD (ie. using assignments instead of assign() statements and children() instead of child()).

It differs from bscheshir's "OpenSCAD bend procedures 2017" in that this, correctly, uses children() for all references to the model being bent, instead of children(0).