gpu chess move generation / perft experiments 

- Move generation uses bitboards
-- position represented using a set of 6 bitboards
-- two variations for sliding piece move generation: kogge-stone and magics
--- three variations of magics: plain, fixed shift fancy, and byte-lookup fancy
--- table sizes: 2.3 MB, 760KB, 150KB respectively.
-- kogge stone faster in some cases and fixed shift fancy faster in some

- perft routine can work with or without transposition table support

- peak speeds on overclocked GTX 780:

-- without transposition tables: 
--- 27 Billion moves per second (pos2 of cpw)
--- 16 Billion moves per second (starting pos)
--- 1.5 hours for perft(10) of start position

-- with transposition tables:
--- start position perft(11) in 1 hour!