[MLton] A4 paper in user guide

[Henry Cejtin]

Yes,  I  thought  about  that  but for people who use the binary packages, it
won't matter (except now they prefer our bugs when it uses A4 by mistake).

I must say, I read a paper describing why the European sizes (A4,  etc.)  are
they  way  they are, and they are MUCH more sensible than our sizes.  The key
point is that if you take a standard size  and  cut  it  into  two  parts  by
halving  the long size, then the aspect ratio does not change.  That requires
that the aspect ratio be the square root of 2.  Truly very nice.