DOM support for Java tidy

I've added *limited* DOM support to Java tidy.  Basically, all you
can do right now is read elements and attributes of the parse tree.  You
cannot modify the parse tree in any way.  I have made fields of
org.w3c.tidy.Node protected, as I would like to phase out
external use of this class, and phase in DOM-style access to the parse
tree.  Note that Java Tidy cannot yet be called DOM-compliant,
but it's getting there.

If anyone wants to build on what I've done for DOM support, I will
look at incorpoarating it into Java tidy.

I will be working on bringing Java tidy up to the 27 Sep 1999 release
of the official tidy next.  Since, I will be busy at my real job in the next
few months, I would appreciate any help that people could offer - if you
want to send me updated source code, I will incorporate that into Java
tidy.

Andy Quick