doc: more manageable changelog

Change-Id: I7e21a1ad2cbef083ff60a3db234dac7ff3931200
fix doc version number

Change-Id: I5c5add76c37a1c3d0d0148a028adafa4b844450b
Update changelog for 2.6

Change-Id: I083688eaebf4a5365b7befee0b71f4a7f33268bc