Fixed memory leak in Crotate

There was a memory leak in Crotate because references were not being decremented (see http://docs.scipy.org/doc/numpy/user/c-info.how-to-extend.html#reference-counting).  The input arguments are converted using `PyArray_FROM_OTF`, but that actually creates new references (PyObject class).  After the data has been used, these references need to be decremented using `Py_DECREF`.