json.cjson: add a submodule that allows lower level access to the cJSON library (constructing JSON trees in memory with null leafs).

vlib/json/cjson/cjson_test.v

@@ -0,0 +1,8 @@
+import json.cjson
+
+fn test_object_with_null() {
+	mut root := cjson.create_object()
+	root.add_item_to_object('name', cjson.create_string('Andre'))
+	root.add_item_to_object('age', cjson.create_null())
+	assert root.print_unformatted() == '{"name":"Andre","age":null}'
+}