Dynamic draw value

Try to avoid repetition draws at early midgame,
this should give an edge against weaker opponents
and reduce draw rate.

Tested for regressions with SPRT[-3, 1] and
passed both short TC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 68498 W: 12928 L: 12891 D: 42679

And long TC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 40212 W: 6386 L: 6295 D: 27531

bench: 7990513
Merge pull request #1 from mcostalba/master

Dynamic draw value