mesh.generate() seems to be required, contra example comments

[mglover]

The shear wall example contains this comment:

.# Generate the mesh now that we've defined all the openings. Pynite automatically generates all
.# meshes when analyzing, but generating it early with give us the chance to work with it prior to
.# analysis.

Other examples have similar comments.

But if I remove the calls the .generate() in my code, the meshes seem to not exist: they're not rendered, calls to max_shear() and max_moment() return None, and the displacements of involved nodes change.

I've put the .generate() calls back in my code and this works for me, but it seems like at a (documentation?) bug.