µcad export API

This crate provides the µcad export API which provides functionality to export µcad model trees into various file formats.

The following exporters are implemented at the moment:

• svg: Export a 2D model as SVG.
• stl: Export a 3D model into an STL mesh.
• ply: Export a 3D model as PLY.
• wkt: Export a 2D model as Well-Known-Text (a simpler format than SVG to represent polygonal geometries).
• json: Export any model as JSON.