Expunge across_dim_types from isl align_foo calls

Closes #198

See merge request inducer/loopy!352

Was deprecated in islpy!13.

Update setup.py to include islpy>=2019.1

See merge request inducer/loopy!350

[bugfix] Do not treat the read_variables field of CInstruction as pymbolic

See merge request inducer/loopy!347

It is expected to be an iterable of strings. Trying to build keys from it
as if it was pymbolic results in raw strings ending up in the pymbolic mappers
(being foreign objects).

Azure: Tweak versions, run twice

Fix integer assoc test

See merge request inducer/loopy!346

Fix multiplicative associativity in expr codegen

Closes #188

See merge request inducer/loopy!344

Do not allow non integral array indices

See merge request inducer/loopy!342