add custom chess engine

native/chess_engine/src/movegen.h

@@ -0,0 +1,17 @@
+// Legal move generation. generate_legal is a method on Position (declared
+// there); this header exists so other translation units can pull in the
+// pseudo-legal generator if they ever want it.
+#ifndef CHESS_MOVEGEN_H
+#define CHESS_MOVEGEN_H
+
+#include "position.h"
+
+namespace chess {
+
+// Generates pseudo-legal moves (ignores leaving your own king in check).
+// Position::generate_legal filters these. Castling is generated fully-legal.
+void generate_pseudo(const Position& pos, MoveList& list);
+
+} // namespace chess
+
+#endif // CHESS_MOVEGEN_H