A solver for the pawns-only chess variant described in:

   http://www.chesscorner.com/tutorial/basic/pawngame/pawngame.htm

Expect to need quite a bit of memory (tunable by changing
TP_TABLE_SIZE in pawnsonly.cpp).

Without en passant, the game would be a draw. With en passant, it
turns out 1. b4/c4/f4/g4 are winning moves for white; all other moves
are wins for black.