Version 1.3 release.

Updates CHANGELOG, version, docs.
diff --git a/googleapiclient/__init__.py b/googleapiclient/__init__.py
index 83862a5..898278d 100644
--- a/googleapiclient/__init__.py
+++ b/googleapiclient/__init__.py
@@ -12,4 +12,4 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-__version__ = "1.2"
+__version__ = "1.3"