[MLton] wiki -> documentation

[Matthew Fluet]

> I added a script (bin/grab-wiki), based on one Vesa sent a while back,
> that downloads the wiki into a self-contained set of documentation
> intended to be shipped with MLton packages.  I put the output of a
> recent run in the svn in doc/guide.  Please check it out and make
> suggestions for improvement.

Would it be worth adding the 'class = "external"' attribute to wiki-links 
that point back to mlton.org?  I'm thinking of Download.  There are also 
all of the "ViewSVN" links.