More sparse operations support

[alyst]

This PR adds support for more SparseMKL operations:

• dense := sparse * sparse (spmmd!(), sp2md!())
• sparse := sparse * sparse (including the in-place one that can optionally disable checks for the sparsity structure) (spmm!(), sp2m!())
• dense := X * A * X^T (syprd!())
• dense := X * X^T (syrk!())

[amontoison]

@alyst Can you split the PR to add what is already working?

[alyst]

@amontoison I will rebase it on top of the 2 PRs I have submitted today. I think all of the new operations should be working (I use them in my code), but I would need to fix/add the tests.

[amontoison]

Perfect, thanks @alyst 👍
What we should also try to interface in the future is the sparse preconditioner.