Added extra stuff about primes (in divideTheory)
and prime factorization (primeFactorTheory). Uses
the notion of a product on finite bags of numbers,
which has been defined in bagTheory.

Prime factorization can also be found in Joe Hurd's

examples/miller/groups/ftaScript.sml

Integrating all the useful goodies from his number
theories into the theories in src looks to be a
substantial but very useful project.

Implementation of sha-1. A good exercise for the word libraries, but
it would be difficult to prove correct.