Allow script authors to load and save documents in their own security context, not the user's.

Right now if you have programming rights, you can save a document which the viewer cannot save. This feature should be available to script authors who don't have programming rights.
Apis are available to the script author but not the viewer so the script author should take responsibility for documents saved through apis.
There should be the possibility to save information about the viewer without the viewer seeing information about other viewers.
We should not need programming rights except in extraordinary occasions.
It is better to add new api than break old.

Proposal:
Add to xwiki.api.Document
saveAsAuthor()
saveAsAuthor(String comment)
saveAsAuthor(String connent, String isMinorEdit)
deleteAsAuthor()

Add to xwiki.api.XWiki
getDocumentAsAuthor(DocumentReference reference)
getDocumentAsAuthor(String fullName)