Port inet_ntop and inet_pton for WIN32

Without these functions, compilation fails on MinGW

src/socket.c

@@ -41,6 +41,59 @@
 #define mrb_cptr_p(o) mrb_voidp_p(o)
 #endif
 
+#ifdef _WIN32
+const char *inet_ntop(int af, const void *src, char *dst, socklen_t cnt)
+{
+    if (af == AF_INET)
+    {
+	struct sockaddr_in in;
+	memset(&in, 0, sizeof(in));
+	in.sin_family = AF_INET;
+	memcpy(&in.sin_addr, src, sizeof(struct in_addr));
+	getnameinfo((struct sockaddr *)&in, sizeof(struct
+		    sockaddr_in), dst, cnt, NULL, 0, NI_NUMERICHOST);
+	return dst;
+    }
+    else if (af == AF_INET6)
+    {
+	struct sockaddr_in6 in;
+	memset(&in, 0, sizeof(in));
+	in.sin6_family = AF_INET6;
+	memcpy(&in.sin6_addr, src, sizeof(struct in_addr6));
+	getnameinfo((struct sockaddr *)&in, sizeof(struct
+		    sockaddr_in6), dst, cnt, NULL, 0, NI_NUMERICHOST);
+	return dst;
+    }
+    return NULL;
+}
+
+int inet_pton(int af, const char *src, void *dst)
+{
+    struct addrinfo hints, *res, *ressave;
+
+    memset(&hints, 0, sizeof(struct addrinfo));
+    hints.ai_family = af;
+
+    if (getaddrinfo(src, NULL, &hints, &res) != 0)
+    {
+	printf("Couldn't resolve host %s\n", src);
+	return -1;
+    }
+
+    ressave = res;
+
+    while (res)
+    {
+	memcpy(dst, res->ai_addr, res->ai_addrlen);
+	res = res->ai_next;
+    }
+
+    freeaddrinfo(ressave);
+    return 0;
+}
+
+#endif
+
 static mrb_value
 mrb_addrinfo_getaddrinfo(mrb_state *mrb, mrb_value klass)
 {