def save_public(filename)
      rc = ffi_delegate.save_public(filename.to_s)
      return if rc == 0
      raise_zmq_err("error while saving to the file %p" % filename)
    end
def save_public(filename)
      rc = ffi_delegate.save_public(filename.to_s)
      return if rc == 0
      raise_zmq_err("error while saving to the file %p" % filename)
    end
Saves the public key to file in ZPL ({Config}) format.
 @param filename [String, #to_s] path/filename to public file
 @return [void]
 @raise [SystemCallError] if this fails