This adds 3D support to the Rotate transformation, and introduces
RotateX, RotateY, and RotateZ for 3D rotations around the x, y, and z
axes.

Ensure the number of transforms equals the number of random states.
Previously, the projection would silently be calculated only for the
number of transforms equal to the number of random states.

* Use `@docs; canonical=false` for documentation outside of ref.md.
  This allows documentation to exist on a second page. Previously,
  documentation was split between multiple pages. Some were in ref.md,
  and some were in other pages (transformations.md, buffering.md). Now,
  all documentation is at least in ref.md, but can also be duplicated
  on other pages with `canonical=false`.
* Add missing documentation to ref.md, and transformations.md.
* Enable the visualizations in gallery.md, and clean up the code a bit.
* Add visualizations in gallery.md for 3D rotations.