Bug 447 - Yang documentation generator improvements

-added summaries at the top of page + linked localy
-added nested child nodes of grouping and augmentation nodes
-added local links between type definitions and their users
-minor fixes

Change-Id: I573f4ee257e66c140e52327534e840801f7b3c5f
Signed-off-by: Milos Fabian <milfabia@cisco.com>
Merge "Bug 447 - Yang documentation generator improvements"