- Unbreak the three broken tutorials (fixes#848)
- This involved a rewrite of PPP-01-10 because I already had my own
solution to that one and I couldn't easily tell what was going
wrong with the previous solution.
- Add assertions to all the tutorials so that non-raising means success
- Add the TTT examples to `test_examples.py` added recently for #909
- Also added sympy to development dependencies since one of the TTT
examples uses it.
Examples changes that were necessary:
- loft.py: failed on macos (only) because of (seemingly) over-precise
floating-point accuracy assertion. Loosened the tolerance, and
expressed it as a multiple of the expected value.
> AssertionError: delta=0.002982314711971412 is greater than tolerance=0.001; got=1306.3375467197516, want=1306.3405290344635
- packed_boxes.py: only emit output files when GEN_DOCS is
True (mimicking lego.py).
