Revert "updated version to 0.9.11"

This reverts commit f5495c55d079e6c8768aed8f8309ebba281c1a61.

This was a bit pre-maturely done since there ended up being some more
commits to go in before the release (and leaving this version change
prior but tagging after would be confusing).
Bump version to 0.9.11.

Update `doc/CHANGELOG.md` appropriately.