new Toom code

[Torbjorn Granlund]

Dominique DELANDE <Dominique.Delande at spectro.jussieu.fr> writes:

  I tested with gmp-chudnovsky and got a 2-3% speedup. Not bad!

I suppose most multiplication in gmp-chudnovsky.c are balanced,
therefore you don't get more speedup.

There is much more headroom, more than a factor 2x is possible by just
improving GMP.

-- 
Torbjörn