Try thrust complex in c++? #147

Followup to issue #6 about complex in cuda, to issue #71 about vectorization, to issue #117 and items discussed there. This afternoon Hadrien's talk https://indico.cern.ch/event/1003975/ mentioned his studies of thrust for c++, nt just cuda. It looks better for vectorization. Not sure it is relevant for us if we use my custom RRRRIIII implementation for vectorization. But could be tried...