std/lib/collections: add Object.get_len(); add some tests for encoding/json

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

lib/std/collections/object.c3

@@ -274,6 +274,14 @@ fn Object* Object.get_at(&self, usz index)
 	return self.array.get(index);
 }
 
+/**
+ * @require self.is_indexable()
+ **/
+fn usz Object.get_len(&self)
+{
+	return self.array.len();
+}
+
 /**
  * @require self.is_indexable()
  **/