A version blocks for attributes

[jjhursey]

It would be nice to mark a section of attributes that were all added in the same version, without labeling each individually. Something like \markversionstart{3.0} and \markversionend{3.0}.

This will be useful in v3 of the standard.

[jjhursey]

In PR #337 we added a more flexible system for adding a marker to the left margin with the \textInMargin command and an update to the \versionMarker command to use it.

If we still want these types of version blocks then we could use a similar mechanism to the Provisional markers.