Pass on keyword arguments for outlier clipping in detrend()

[ekaterinailin]

The keyword arguments outlier_sigma and outlier_mwidth are not passed on into detrend()
I think they should go somewhere in here:

Lines 122 and following:

## Iterative sigma-clipping
        ## ------------------------
        print('Starting initial outlier detection')
        omask = mask & sigma_clip(cflux, max_iter=10, max_sigma=5, mexc=mask)
        ofrac = (~omask).sum() / omask.size
        if ofrac < 0.25:
            mask &= omask
            print('  Flagged %i (%4.1f%%) outliers.' % ((~omask).sum(), 100*ofrac))
        else:
            print('  Found %i (%4.1f%%) outliers. Not flagging.' % ((~omask).sum(), 100*ofrac))

Your maintenance work is very much appreciated!