- fixed "make distrib"
- updated CHANGES
- changed version number to 0.72

Counter-example: gcd 4 (4 mod 2) = gcd 4 0 = 4 <> 2 = gcd 4 2.

Note that the "divides" definition from the theory is overridden with a
notation, which happens to be equivalent.

Generating the documentation was not working since the symbols read by
why3doc in local files were not the ones that had been globalized from
installed files.

{h ... }: html escape
[ ... ] : Why3 code escape