fixed documentation titles

modules/face/doc/face.rst

 ***************************************
-contrib. Contributed/Experimental Stuff
+face. Face Recognition
 ***************************************
 
 The module contains some recently added functionality that has not been stabilized, or functionality that is considered optional.

modules/optflow/doc/optflow.rst

 ******************************************
-text. Optical Flow Algorithms
+optflow. Optical Flow Algorithms
 ******************************************
 
 .. highlight:: cpp

modules/reg/doc/reg.rst

 **************************
-reg. Registration
+reg. Image Registration
 **************************
 
 .. toctree::

modules/xfeatures2d/doc/xfeatures2d.rst

-***************************************
-features2d. Extra 2D Features Framework
-***************************************
+*****************************************
+xfeatures2d. Extra 2D Features Framework
+*****************************************
 
 .. highlight:: cpp
 

modules/xphoto/doc/xphoto.rst

-**********************************
-xphoto. Addon to basic photo modul
-**********************************
+***********************************************
+xphoto. Additional photo processing algorithms
+***********************************************
 
 .. toctree::
     :maxdepth: 2