Continued code redesign for the DocumentImpl class. Now the "delete" and
"write" methods are static, so a DocumentImpl objject need not be created
in order to initiate a INSERT, UPDATE, or DELETE action (it is created
implicitly by the DBSAXHandler). When doing a "READ" action, one still
creates a new DocumentImpl instance which represents the document that
was read from the db (and calling toString() on it returns an XML
serialized version of the DocumentImpl).
This brings us close to being able to use the DocumentImpl class as a
DOM Implementation of the DOM Document interface.