Better error messsages when asking about orientation of non-volume meshes

See merge request inducer/meshmode!55

Tweak object array treatment in separate_by_real_and_imag

See merge request inducer/meshmode!53

Avoid on-the-fly gmsh generation, to avoid flaky CI--e.g....

See merge request inducer/meshmode!52

Avoid on-the-fly gmsh generation, to avoid flaky CI--e.g. https://gitlab.tiker.net/inducer/meshmode/-/jobs/69357)

Add mesh_to_tikz

See merge request !50

Get tags from gmsh

See merge request inducer/meshmode!49

set facial_adjacency_groups to only compute once needed, even with boundary tags provided at construction of mesh

Use canned meshes for boundary convergence test

See merge request inducer/meshmode!48

Address invalid value encountered in generating urchin mesh

See merge request inducer/meshmode!45

Placate flake8 3.6

See merge request inducer/meshmode!47