Archive - before attribute migration system

Archive Silk as is (functional) before implementing the attribute migration system.

All Silk objects in existing documents are incompatible with the new attribute setup. All existing Silk document objects will be automatically migrated by future versions of Silk.

This version is released as an archive in case of unexpected issues in the new attribute handling system.

All Silk document objects will thereafter track object version numbers. In future versions of the workbench (under current development), attributes will be reorganized, and new attributes will be added.

versioning:
-existing document objects will be examined when the documents are opened.
-if no version attribute exists, the object is migrated to the latest attribute set.
-thereafter, existing objects will be checked every time a document is opened.
-if the existing object version is out of date, the object will be updated.

new attributes (examples):
-nearly all Silk objects will receive a 'tolerance' attribute (float)
-many Silk objects will receive a 'reverse' attribute (boolean)
-all Silk objects will receive a 'version' attribute, to track whether or not they have the latest attribute set