tiles-stems imported pandas, an optional dependency, to write its CSV, so
the release workflow's test job (which does not install it) failed and
v0.3.0 was never published. It now uses the csv module, and the CLI test
checks the file's rows.

Notebook 18 shows buttress detection, meshing and fusing on two real trees
from the destructive-harvest data of Burt et al. 2021: 3D views of the
points, sections of the flanged base against the mesh, the mesh from two
sides, the cylinder model it replaces, and one fused mesh of the whole
tree. make_buttress_subset.py cuts the two small data files from the ray
clouds. The QSM guide, examples index, data README and references link to
it.