Add multi-object and multi-group support for OBJ files

[benjaminwgordon]

Wavefront .obj files can contain multiple objects in a single file. Additionally, objects can be constructed from several groups of Polygon Paths.

The current implementation presumes a single object and group in the file for parsing.

holographit/holoscribe/src/main.rs

Line 41 in 4fc3854

for simple_poly in obj.data.objects[0].groups[0].polys.clone() {

This should be extended to support multi-object and multi-path to allow constructing holograms for more complex shapes.