Implement Spartan Chess

Implement Spartan Chess

This required new pieces, their parsing in algebraic moves and promotions,
a lot of promotion code because Hoplites can promote, implementation of
the duple-check rule by letting in_check recursively call itself after
abdicating the first king, making the test for nr of kings less critical,
and choosing a promotion piece in the mate test (because promotion to K
could solve the mate).