Function libwebp_sys::WebPAnimEncoderAdd

pub unsafe extern "C" fn WebPAnimEncoderAdd(
    enc: *mut WebPAnimEncoder, 
    frame: *mut WebPPicture, 
    timestamp_ms: c_int, 
    config: *const WebPConfig
) -> c_int

This is supported on crate features mux and 0_5 only.