Clean up interp extension module.

Pass the arrays directly into it, don't use clobbered numpy pointers.

Don't need to import libgsl or libgslcblas from Python - these library
dependencies will be handled by distutils at compile time.

Don't extract the interpolation type in Python, let the extension module handle
that.
Update references of PyArray_FromDims to PyArray_SimpleNew (former is deprecated)
Convert the svd C shared library to a Python extension module.

Include a simple unit test for SVD.