[MLton] MLton library project licensing

[Stephen Weeks]

> This looks good.  You should be seeing some commits coming in for the
> library project soon enough :)

Great.  We never did settle on a place.  I think that it would be best
to create a new toplevel project in the repository, parallel to the
mlton project.  I proposed

  svn://mlton.org/mltonlib

Since there were no objections, I've gone ahead and created it, with
the standard {branches,tags,trunk} subdirectories.