Added children function

Allows to retrieve children of a file record.

pillarsdk/files.py

@@ -37,3 +37,17 @@ class File(List, Find, Create, Post, Update, Delete, Replace):
         url = utils.join_url(self.build_previews_server_path, path)
         api.get(url)
         return self.success()
+
+    def children(self, api=None):
+        """Collect children (variations) of the current file. Used to connect
+        different resolutions of the same picture, or multiple versions of the
+        same video in different formats/containers.
+
+        TODO: add params to support pagination.
+        """
+        api = api or self.api
+        files = self.all({'where': '{"parent": "%s"}' % self._id}, api=api)
+        print files._items
+        if not files._items:
+            return None
+        return files