Added is_modified feature to json_t struct

Added is_modified field to json_t struct along with getter and setter
methods.

src/jansson.h

@@ -50,6 +50,7 @@ typedef enum {
 typedef struct json_t {
     json_type type;
     size_t refcount;
+	boolean is_modified;
 } json_t;
 
 #ifndef JANSSON_USING_CMAKE /* disabled if using cmake */
@@ -78,6 +79,7 @@ typedef long json_int_t;
 #define json_boolean_value     json_is_true
 #define json_is_boolean(json)  (json_is_true(json) || json_is_false(json))
 #define json_is_null(json)     ((json) && json_typeof(json) == JSON_NULL)
+#define json_is_modified(json) ((json)->is_modified)
 
 /* construction, destruction, reference counting */
 
@@ -129,6 +131,8 @@ typedef struct {
 
 /* getters, setters, manipulation */
 
+int json_set_modified(json_t *json_object, bool input);
+
 void json_object_seed(size_t seed);
 size_t json_object_size(const json_t *object);
 json_t *json_object_get(const json_t *object, const char *key);

src/value.c

@@ -44,6 +44,11 @@ static JSON_INLINE void json_init(json_t *json, json_type type)
 }
 
 
+int json_set_modified(json_t *json_object, bool input)
+{
+	json_object->is_modified = input;
+}
+
 /*** object ***/
 
 extern volatile uint32_t hashtable_seed;