[plt-scheme] DrScheme online syntax highlighting

First stab at http://dsweb.hopto.org/scheme-highlight.tar.gz

To use: untar and gunzip the archive in collects/highlight, then restart
DrScheme.  Syntax highlighting is local to the last expression typed, so
you won't see any colors right after loading a file.  I hope it's faster
this way; please let me know if it's still too slow.

I don't know what the error messages that pop up sometimes when you open
a file mean -- with-handlers doesn't catch them so I don't know where
they come from.

By the way, I noticed that there is a syntax-color collection.  How does
that work?

Daniel