API doc for Extra route extension

Added doc for extra route extension
Fixes bug 1157156

Change-Id: Ic15608d020296fcdc0d04c8e7c58ac71310e218f
Added security-groups and security-groups-rules extensions

bug: #1108119

Change-Id: I13f69f8c91493f3a0bbd3daec6b4cee9cf676da3
author: Sameer Satyam/Diane Fleming