Function libthemis_sys::themis_secure_message_sign

pub unsafe extern "C" fn themis_secure_message_sign(
    private_key: *const u8, 
    private_key_length: usize, 
    message: *const u8, 
    message_length: usize, 
    signed_message: *mut u8, 
    signed_message_length: *mut usize
) -> themis_status_t