in power_operator repleced len(set(pindex)) by max(pindex); pseudo info commented out and else added to projection_operator.pseudo_tr; several AttributeError changed to NotImplementedError.

fixed: kwarg forwaring to draw_vector_nd; size keyword removed; power_operator.get_random_field replaced by super.

powerspectrum.calc_ps_fast optimized; nifty_core adjusted; power_operator.get_power optimized by introduction of a power un(in)dex; weight_power added to nifty_power; docstrings revised.