Moved ancillary files to extras/ (fixes #1011)

extras/tests/Misc/Issue978.cpp

@@ -0,0 +1,13 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2019
+// MIT License
+
+#include <ArduinoJson.h>
+
+struct Stream {};
+
+int main() {
+  Stream* stream = 0;
+  DynamicJsonDocument doc(1024);
+  deserializeJson(doc, stream);
+}