Parallel joist/mullion/rafter repeats

[brunopostle]

The perl Homemaker code had repeating beams filling a 'slab' space, this was used for rendering pergolas.

This needs to be reintroduced in a more general way for roof rafters, glazing mullions, pergolas, floor joists etc..

Roof and soffit slabs are already oriented in 2d with up = y, floor slabs will need to be oriented to the shortest side parallel to y.

Parallel elements will need to be cropped to the slab extents.

Unlike the 'Repeat' module, elements should have regular spacing rather than equal spacing.

Elements will be extruded profiles, but should allow nesting, horizontal/vertical orientation (for transoms), and repeating non-extrusion assets.

For example it should be possible to model a patent glazing system with regular mullions and transoms, infill glazing and fixings.

For roofs, some attempt should be made to align the grid in adjacent faces when the pitch is uniform.