Bezier library for OpenScad

**IMPORTANT** This library is not user friendly. It a lot easier to use with the SVG to OpenSCAD InkScape extension.
See: https://www.thingiverse.com/thing:2805184

Another useful tool to create incredible models with OpenSCAD. I added a module to create a single polygon from a list of points and bezier handles.

The modules provided by the original version (http://www.thingiverse.com/thing:8483) are nice when we are trying to control how the polygon will be split into triangles, but they are not useful when trying to create a polygon to use with rotate_extrude.

The only modifications I made to the original library is to add the module ```bezier_polygon``` to create a single polygon from a list of point, and I fixed a few deprecated usages.

**[2017-03-13]** I updated the ```BezPolygon``` module. I added a boolean parameter to show the points and bezier handles. Those are quite useful when drawing a complex polygon manually, or when editing one. This feature is not intended t