Callbacks to implement Event Emitters

luv_server_t* luv_server_create(
      uv_loop_t *loop
    , const char* host
    , int port
    , luv_onclient_connected onclient_connected
    , luv_onclient_disconnected onclient_disconnected
    , luv_onclient_msg onclient_msg) {

  luv_server_t *self          = malloc(sizeof(luv_server_t));
  self->host                  = host;
  self->port                  = port;
  self->num_clients           = 0;
  self->onclient_connected    = onclient_connected;
  self->onclient_disconnected = onclient_disconnected;
  self->onclient_msg          = onclient_msg;
}