color: document that changeset phases have labels It's very useful to be able to colourise csets according to their phases. There was no indication anywhere in the docs that this is possible. We use e.g. `changeset.secret = ` instead of `changeset.secret ='none'`, because otherwise this is a BC: it would nullify the effects given to log.changeset label that usually surrounds the changeset.{phase} labels. Specifying the label without any effect instead of 'none' is a true no-op change and purely documentation.