ENH: Complex integer and/or fixed point dtypes #260

In numpy/numpy#12184 there is a discussion about fixed point and integer dtypes. Would there be any interest in them here? I think there is some preliminary work with older APIs in @WarrenWeckesser's https://github.com/WarrenWeckesser/numtypes. The main use of this seems to be for signal processing, so it would need fft/linalg support.