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 !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