Implementation of spdiagm for CUSPARSE

[walexaindre]

Here is the implementation of SparseArrays.spdiagm(vec)

The one(Int32) and Int32 conversions are used to reduce allocations and enhance the performance of this simple function.

Closes #1857

[amontoison]

Can you add a test for your implementation of spdiagm?

[walexaindre]

Thank you @amontoison for looking at my PR. I can implement that test but I am confused about where I need to do that exactly.

Can you suggest me a possible file where I can write that test?

I was thinking about generic.jl or interfaces.jl. However, generic.jl looks like a place where some basic operations between matrix and vectors are tested and interfaces.jl looks like a file where linear algebra related functions are the main theme.

I belive that interfaces.jl could be the correct place. But if you can shed some light on the logic behind file organization and where it is expected to implement something like this, I would appreciate it.

[walexaindre]

For now, tests are implemented as a new test section in interfaces.jl

[amontoison]

For now, tests are implemented as a new test section in interfaces.jl

The test files interfaces.jl and linalg.jl are fine.
LGTM!