[MLton] mingwows

[Andrew Kennedy]

First, thanks very much to Wesley and everyone else involved for making
mlton work under MinGW. I've been compiling our SML.NET compiler
successfully using it, with excellent performance.

Second, please *do* include mlton.bat. Compared to cygwin, I very much
like the minimal install associated with the MinGW version: just install
MinGW with appropriate components, put the mlton distribution into a
C:\mlton directory, set your path, and away you go. No messing with
environment variables and paths and whatnot. Why would you *not* include
the mlton.bat script? (Though, I can see that a mlton.exe would be even
nicer).

- Andrew.