Cython api for lapack and blas

- [x] Add interface for lapack and blas routines.
- [ ] Add working example in tests
- [ ] Review signatures for correctness
- [ ] Add function to get directory of `scipy.linalg` (similar to `numpy.get_include`)
- [ ] Finish wrappers for 'gees' and 'ggees' functions.
- [ ] Add interfaces to the functions added in https://github.com/scipy/scipy/pull/3984
- [ ] Add this api to the documentation
If I understand correctly, these numbers all depend directly on the definitions of IEEE floating point arithmetic, so they should be safe on all platforms. On the other hand, it would probably be safer to call the Python wrappers anyway to avoid unnecessary test failures in bizarre environments. I'll do that instead.