Improve KBPsK endgame

Better endgame with bishop and blocked g-pawn

bench: 8279065
Add some knowledge for KRPKB endgame

bench: 8279065
Add helper function verify_material

Allows to remove a lot of assert code in endgames.

No functional change.
Massive stronger/weaker renming

No functional change.
Remove a drawing rule from KBPsK function

The rule can be incorrect if the attacking king is
well placed e.g. 8/6K1/8/8/7k/1B6/7P/8 w - - 0 1

bench: 8279065
Merge pull request #7 from mcostalba/master

merge