Update release notes for 0.3.1

* update README
* fix doc errors

Change-Id: I5682654bf482289879c8ba9016e348f2b2782971
Merge branch 'review/terry_howe/bug/1100116' into dt-test
Merge branch 'review/terry_howe/bug/1256935' into dt-test
Merge branch 'release-0.3.1' into dt-test
Merge branch 'oslo-clean' into dt-test
Merge branch 'image-v2-v2' into dt-test
Merge branch 'identity-ec2-tests' into dt-test