Add getaddrinfo.pyx demo

src/getaddrinfo.pyx

+from stdlib.string cimport Str
+from stdlib.socket cimport getaddrinfo
+
+from libc.stdio cimport printf, puts
+from libc.string cimport strlen
+
+def main():
+    with nogil:
+        l = getaddrinfo(NULL, Str("3490"), 0, 0, 0, 0)
+        for a in l:
+            s = a.sockaddr.to_string()
+            printf("%d %d %d %s %s\n", a.family, a.socktype, a.protocol, Str.to_c_str(a.canonname), Str.to_c_str(s))
+
+main()
+