Allow turning off SPEX python interface

[rayegun]

There's currently no way to turn this off when building shared libs, and it would be cleanest to allow turning it off at the SuiteSparse level, not just the SPEX level.

[mmuetzel]

Looks good to me.

Should the new CMake parameter be named SUITESPARSE_USE_PYTHON (or SUITESPARSE_ENABLE_PYTHON) to better fit the naming convention that is being used for recent changes?

[rayegun]

Good point, updated the naming

[mmuetzel]

It would probably be nice to document the new variable. Maybe, around here?

SuiteSparse/SuiteSparse_config/Config/README.md.in

Line 982 in 00863cd

* `SUITESPARSE_USE_OPENMP`:

[DrTimothyAldenDavis]

yes, adding something to the top-level README would be a good idea. Also in the SPEX/README.

I have some other changes to SPEX that are pending, in the paru_dev2 branch. I'm making some major changes to ParU in that branch, and while I was working on that I found some issues with SPEX when building the MATLAB interface. I'll rebase this to the paru_dev2 branch and merge it there.

Then I, or @rayegun, could add the README updates to paru_dev2.

Alternatively, I could do a PR of paru_dev2 into dev2, but I'm hesitant to do that just now without resolving some of the other PRs to dev2 just now.

[DrTimothyAldenDavis]

Correction: I'll go ahead and merge this into dev2 and then keep paru_dev2 updated with PRs from dev2 to paru_dev2. Less churn that way.

Also: I will rename this as SUITESPARSE_USE_PYTHON since the _USE_ style is used for all other options like this one.

[DrTimothyAldenDavis]

Updated with this commit:

8d59151