Initial commit for nimrod solver

A new solver written in Nimrod.  I'll be storing possibilities
by row, column, and block this time instead of per cell which should
let me do several things more effectively including trying un-forced
values without having to copy first.

I'm taking advantage of Nimrod's set support, as well as it's
interesting compile-time evaulation features to create indices into the
overall sudoku for row, column, and block addressing.