Adding BGPCEP chapter to Developer's Guide

This is just Shahida's patch with a few tweaks by Colin Dixon to get it
to build.

Change-Id: Id6723c707cfa9f6c2e4873360d3b66f5a9ce201e
Signed-off-by: Shahida <sthiruva@brocade.com>
Signed-off-by: Colin Dixon <colin@colindixon.com>
Merge "Adding BGPCEP chapter to Developer's Guide"