Fix skipped lines in doctest

During the migration to compas 2.0 via the branch https://github.com/compas-dev/compas_fab/tree/support_private_data .
A number of Examples in the docstrings were throwing errors due to a new `__str__` implementation in compas core.

These strings were skipped from the automated `doctest` (locally: `pytest --doctest-modules`) in order to move forward. It is likely that compas core will change the behavior of `__str__` to have shorter prints, similar to (https://github.com/compas-dev/compas/pull/1234).

These skipped tags should then be removed. Search for the term `# doctest: +SKIP` in order to find them.