Notation model could benefit from versioning.

[jamestunnell]

The code is very sensitive to changes in the notation model. Of course the current notation model will at some point need to be solidified before a real initial release can be made. To allow for changes to the notation model, a separate versioning scheme could be implemented, with any changes to the model accompanied by methods for upgrading previous versions of the model to the latest version. Of course the code would always be updated to operate on the latest notation model version.