Raise an error when non-CL-array passed to discr conn (Closes #8 on gitlab)

Closes #8

See merge request inducer/meshmode!27

affine_map einsum compatibility

See merge request inducer/meshmode!26

Silence loopy language version warnings

See merge request inducer/meshmode!25

einsum changed arrays from C_CONTIGUOUS to F_CONTINGUOUS, which got sent
to map_mesh above and reshaped into an array that wasn't C or F
contiguous.

Ensure nodes are C-contig in merge_disjoint_meshes even with numpy 1.14

See merge request inducer/meshmode!24

# Conflicts:
#   .gitlab-ci.yml

Switch spuiously (?) failing AMD CPU test to Intel

See merge request inducer/meshmode!23

Switch gmsh reading from meshpy to gmsh_interop

See merge request inducer/meshmode!22

Create element group base class to indicate interpolatory-or-not

See merge request inducer/meshmode!21

Same-mesh connection: allow 'interpolating' for non-interpolatory groups if nodes are exactly identical

Fix an unbound variable in ChainedDiscretizationConnection.

See merge request inducer/meshmode!20

Also test ChainedDiscretizationConnection, because it doesn't
look like it is being tested.

Rename FRESTR symbols to something more self-explanatory (thanks @eshoag2)

See merge request inducer/meshmode!19

Change ALL_FACES to FRESTR_ALL_FACES and INTERIOR_FACES to

See merge request inducer/meshmode!18

FRESTR_INTERIOR_FACES in a few documentation spots.

(Noticed by Li Lu.)

Documentation fixes / Discretization doc improvements

See merge request inducer/meshmode!17

pointing this out).