Implement 9 x 9 grid board

[ghost]

This helps with three things:

1) piece handling 2) teaching people how to play (easier to start) 3) smarter AI

[ghost]

Rule Changes

Going from Feltar 11x11 to Skalk 9x9, two rules change to keep the game balanced:

1) King is captured by only two pieces 2) King can be captured against an edge

NOTE: Skalk is the closest one to Feltar. Even with these changes, Black as big advantage, which is great. Our AI can use the edge. We'll frame the game as user playing white.

References: See http://aagenielsen.dk/hnefatafl_rules_overview.html. http://aagenielsen.dk/hnefataflforum/viewtopic.php?f=4&t=203

Other 9x9 Tafl games:

• Foteviken Tablut 9x9
• Ealdfaeder Hnefatafl 9x9
• Longship Tafl (Sea Battle Hnefatafl) 9x9

[apotapov]

Implemented Skalk without edge capture.