Info: Private improvements for anyone being interested

[achimste]

Hi everyone!

I made a lot of changes to the chess lib and keep them in a branch improvements in my fork.
I invite everyone being interested to take a look at my changes. Those are so many, that I cannot bulk-PR them here.

What I did so far in general terms:

• Speedup of many functions.

• Added Bitboard |&^ Square operations like in SF. This removes the need of using Bitboard::fromSquare(...) and shortens the code

• Refactor of Board::prev_states_: It has been replaced with states_. So all those parameters that cannot be reconstructed or recalculated too costly will go into its own state (like SF). This has the advantage that it requires less copying of parameters. A simple pop_back() will get you the old state in unmakeMove.

• Added extended Board::pieces functions that accept two PieceTypes. We often need the bitboards of rooks and queens or bishop and queens together. So this shortens the code.

• External programs often need the checkmask and pin information. I will put these as additional info to the state. So these informations won't be private within the code but visible for the user.

• Introducing pext for magic bitboard -> speedup of slider attacks. This can be disabled (old usage) with a macro.

• Also the initSliders of the magic bitboards is completly refactored by using a template for bishop and rook attacks -> simple few lines of code instead of two bulky functions.

• Added more operators for some classes to make loops more easy.

• Personal taste: I have removed ALL static_cast instructions as those blow up the code. I prefer "old" C-Style conversion.

So... If you are interested in it, leave me comment. I'd be happy to here from you.

Greetings
Achim