The C standard gurantees that an unsigned short is at least up to 65535
huge. Enough to store every TCP port. Also the parameter PORT is
overgiven to the `htons()` function which assumes that the parameter is
of type `uint16_t` which unsigned short is on most platforms.
static const char MESSAGE[] = "Hello, World!\n";
-static const int PORT = 9995;
+static const unsigned short PORT = 9995;
static void listener_cb(struct evconnlistener *, evutil_socket_t,
struct sockaddr *, int socklen, void *);