These were removed from the build because they were not being tested. They were, in fact, very useful to some people, so this commit reinstates them.
They are not included in the main flow of the instructions, but are mentioned in the customisations page.
I have also modified
optics_configurations.scad to allow 35mm parfocal optics to be built. This is not done by default, but there are instructions on how to do it. In the future, perhaps we could move alternate optics modules into another repository, or at least move the building of them into another repo.
Finally, I fixed a regression introduced by the optics refactoring, that resulted in unprintable structures in the tube lens gripper (#268 (closed)).