[kepler-dev] URLS with ptdoc: now bring up the new documentation

[Christopher Brooks]

I modified HTMLViewer so that if a URL begins with ptdoc:
then we bring up the new documentation infrastructure.

I modified whatsNews6.0.htm to use this infrastructure.

Open issues:
1) Not all classes have ptdoc documentation.
don't, we bring up the DocBuilder.  We should be smarter
about this.  For instance
ptdoc:ptolemy.actor.gui.WelcomeWindow does not have PtDoc documentation
because it is not used in a model.  WelcomeWindow does not extend
NamedObj.  I guess we'd like to either generate documentation for it
or else just link to the Javadoc.

2) I'm thinking we should refactor all the ptdoc stuff into its
own package: ptolemy/actor/gui/ptdoc.  One reason is to avoid
making ptolemy.actor.gui depend on Vergil.  Another reason is that
we have classes all over the place: vergil.basic, vergil.actor,
actor.gui, moml.filter.

Perhaps The DocML dtd should probably be renamed to to PtDocML.  I'm
sure there are other DocML dtds out there.

3) We need to make the DocBuilder smarter so that the user can
just refer to docs on the Ptolemy website instead of building their
own.  The reason is that building the docs requires that configure
be run and that make be present.  We could try to come up with 
an ant task and run it from eclipse but the problem is that we need
to pick and choose what packages are available on the local machine.
I think we should just offer the user the possibility of using
the docs on the Ptolemy website.

_Christopher