DOC: cython example producing numpy deprecation warning
Didn't test it out myself, but it appears already for a while in the doc building on Travis. Is this due to our implemenation of the example? Or something with the cython version?

@hayd I think you added this example?

```
reading sources... [ 30%] enhancingperf

In file included from /home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/ndarraytypes.h:1761:0,
from /home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/ndarrayobject.h:17,
from /home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/arrayobject.h:4,
from /home/travis/.cache/ipython/cython/_cython_magic_1f237dce7a3469976da887b4cf262e55.c:314:
/home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/npy_1_7_deprecated_api.h:15:2: warning: #warning "Using deprecated NumPy API, disable it by " "#defining NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION" [-Wcpp]
/home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/__multiarray_api.h:1629:1: warning: ‘_import_array’ defined but not used [-Wunused-function]
/home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/__ufunc_api.h:241:1: warning: ‘_import_umath’ defined but not used [-Wunused-function]

In file included from /home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/ndarraytypes.h:1761:0,
from /home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/ndarrayobject.h:17,
from /home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/arrayobject.h:4,
from /home/travis/.cache/ipython/cython/_cython_magic_91937760ba0c84b679e9c511ddce92eb.c:314:
/home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/npy_1_7_deprecated_api.h:15:2: warning: #warning "Using deprecated NumPy API, disable it by " "#defining NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION" [-Wcpp]
/home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/__multiarray_api.h:1629:1: warning: ‘_import_array’ defined but not used [-Wunused-function]
/home/travis/virtualenv/python2.7.6/lib/python2.7/site-packages/numpy/core/include/numpy/__ufunc_api.h:241:1: warning: ‘_import_umath’ defined but not used [-Wunused-function]
```
