Function mupdf_sys::fz_open_thunder

pub unsafe extern "C" fn fz_open_thunder(
    ctx: *mut fz_context, 
    chain: *mut fz_stream, 
    w: c_int
) -> *mut fz_stream

4bit greyscale Thunderscan decoding from the chained filter. Decodes lines of w pixels to 8bpp greyscale.