Make facet methods chainable.

google/refine.py

@@ -70,13 +70,16 @@ class TextFacet(Facet):
             if s['v']['v'] == value:
                 return
         self.selection.append({'v': {'v': value, 'l': value}})
+        return self
 
     def exclude(self, value):
         self.selection = [s for s in self.selection
                           if s['v']['v'] != value]
+        return self
 
     def reset(self):
         self.selection = []
+        return self
 
 
 class StarredFacet(TextFacet):

google/test/test_engine.py

@@ -79,6 +79,8 @@ class FacetTest(unittest.TestCase):
         self.assertEqual(len(facet.selection), 1)
         facet.reset()
         self.assertEqual(len(facet.selection), 0)
+        facet.include('element').include('element 2')
+        self.assertEqual(len(facet.selection), 2)
 
     def test_reset_remove(self):
         text_facet1 = TextFacet('column name')