Code refresh + minor performance improvements.

[Sundow]

1. Using BitMatrix instead of bool[][] for grid (memory consumption)
2. Using Stopwatch instead of testing Run class for time counting: removes a dependency on testing code from actual logic classes.
3. Replaces LinkedList with List in some places where it was not strictly needed (memory/performance)
4. stack allocation of small local arrays in a couple of places (performance)
5. Code refresh to newer coding standards/language features here and there.

This is a set of changes I did while looking at the code and evaluating if it can be used and an inspiration and/or starting point for my own development. I understand that the original author's view on the coding style and approaches can differ from mine. So, if it doesn't suit the author's view and can't be approved - no hard feelings on my side. In case of any question the author knows where to find me :-)