Missing sparse modules

[david-cortes]

Would be nice if this package would also include the sparse matrix and sparse blas modules from GSL.

[twiecki]

Feel free to add them with a PR.

[david-cortes]

Question about the tests: are they somehow connected to the tests from the GSL library? I see the examples here are exact translations of GSL's examples, but I'm wondering about the tests as they don't seem to match.

[twiecki]

I didn't write them so I actually don't know how they came to be.

[david-cortes]

Created pull request: #32

[david-cortes]

A small comment: I'm using the sparse modules from SciPy in one of the tests that I created, so that's a new dependency to add to the tests.