Add Tord's polynomial material balance

Add Tord's polynomial material balance

Use a polynomial weighted evaluation to calculate
material value.

This is far more flexible and elegant then applying
a series of single euristic rules as before.

Also correct a design issue in which we returned two
values, one for middle game and one for endgame, while
instead, because game phase is a function of board
material itself, only one value should be calculated and
used both for mid and end game.

Verified it is equivalent to the tuning branch results with
parameter values sampled after 40.000 games.

After 999 games at 1+0

Mod vs Orig +277 =482 -240 51.85%  518.0/999  +13 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>