Fix skipped lines in doctest

[yck011522]

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 (compas-dev/compas#1234).

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