OpenScad Revoloids version 0.7

Inching closer to perfection.

This thing is an update to the revoloids library.

This time around, I've gotten the normals calculated correctly, so that a 'shell_extrude' can be performed. So, now there are two methods in the revoloids.scad file: linear_extrude_revoloid, shell_extrude_revoloid

The first one will 'intrude' towards the center of rotation. that's a nice valid way of doing things, but the ends must be relatively flat or things will get messed up.

The shell_extrude, whic