Add Torus as boundary Feature

[BHill96]

It is currently used to draw vortex rings pre-sim, but would be a cool object to add. This would require #6 to be implemented first to use for generate_draw_geom.

[markstock]

It sounds like having a non-class set of functions for geometry generation: cube/rectangle, sphere, and torus would go there. It would accept some basic parameters and return an ElementPacket. Let another function scale, rotate, and translate them into position.