add basic uri sanitization

disallow .. in uri.

src/handler.c

@@ -44,9 +44,12 @@ static int tip_client_file_not_found(struct tip_client *cli)
 	return -1;
 }
 
-/* TODO: sanitize uri, don't escape directory serving files. */
 static bool sanitize(const char *uri)
 {
+	/* TODO: smarter sanitization. */
+	if (strstr(uri, ".."))
+		return false;
+
 	return true;
 }