Move <notes> into an <extension>

[cannin]

@ibalaur @amazein It looks like "notes" such as author information is inserted after . It would be better to insert it into an tag. The idea has been that we will not try to validate things in because they are not necessarily "official".

[amazein]

Thank you, Augustin. This seems to be fairly easy to address, we just need some to find som minimal resource for this task.