Finalisation of revision API. Added _asHTML private method so that BaseURL...

Finalisation of revision API. Added _asHTML private method so that BaseURL support is possible without infinite recursion. Added updateMetadata method to base format API.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@13774 20353a03-c40f-0410-a6d1-a30d3c3de9de