wordladder - code improvement

[mark]

Thanks for your implementation.

I can't use the levenshtien distance because although it is a 
better solution, I want to keep the implementation as compatible 
with those in the other languages as possible.

Your main() is much shorter than mine, but doesn't match the 
behaviour (and again I want to keep the same as the other 
implementations). Nonetheless, I didn't know about generate!()(), 
so I've learnt from yours.

Nor did I know about the StopWatch which I'm now using, plus I've 
added your static assert, and also copied your idea of making 
update() an inner function (and now only needing one parameter).

I still need to study your genLadder() more carefully to 
understand it because it is so compact.