urequests: Add example_xively.py as very basic example.

The main purpose is actually to show the need to call .close().

urequests/example_xively.py

@@ -0,0 +1,16 @@
+try:
+    import urequests as requests
+except ImportError:
+    import requests
+
+r = requests.get("http://api.xively.com/")
+print(r)
+print(r.content)
+print(r.text)
+print(r.content)
+print(r.json())
+
+# It's mandatory to close response objects as soon as you finished
+# working with them. On MicroPython platforms without full-fledged
+# OS, not doing so may lead to resource leaks and malfunction.
+r.close()