changes between R2RML v1.38 and v1.40 drafts

Recent changes:

Version 1.39

    * rr:tableOwner property was marked as optional (Action 103, Issue 23)

Version 1.40

    * backslash for escaping curly braces in values for rr:template
      property (Issue 8 - Curlies)

Thanks,
- Souri/Seema.