missing example for using vector types defined in cltypes

Looks like there's no example using vector types defined in cltypes while the doc itself for these types are not so understandable. There are many examples having kernels taking vector type arguments, but the python code is using the `numpy` type, instead of the defined vector type. E.g. https://github.com/inducer/pyopencl/blob/master/examples/demo_elementwise_complex.py