TODO

Tasks in progress:
   
    - Implement the complete Winboard/Xboard protocol:
      http://www.tim-mann.org/xboard/engine-intf.html
    - Better evaluation function:
      - more mobility evaluation
      - Detect draws by material and likely draws by material (i.e. KR vs. KR).
        This detection should happen in search() if possible.
    - Full support for the PGN standard, including FEN strings


Deferred tasks:
   
    - Try returning alpha or beta even with mate scores
    - Use a bitfield for move instead of an integer
    - Use the BigTwo1 replacement scheme in hash table:
      http://www.xs4all.nl/~breukerd/thesis/summary.html
    - In critical parts use <unsigned> instead of <int> if possible
    - Scale the 7th rank eval bonus with the opponent's pawn material (the more
      pawns it has the bigger the bonus)
    - make_move() should return a boolean value <is_check>.
    - Add a command stack to struct Chess so that all the waiting non-urgent
      commands can be executed when we're done searching.
      UPDATE: turned out that no input ever needs to wait.
    - Evaluation masks (passed pawns etc.) should be grouped in a struct
    - Include ECO code and round number in the PGN log
    - Use the "struct" keyword instead of the typedef name when declaring
      variables in header files (eg. AvlNode *book in Chess).
    - Use a lot more enums like Color, Square, Piece, etc. On the other hand,
      enums aren't enforced so let's drop this plan.
    - Add a global <notation> setting. It should accept values:
      - NTN_SAN   - use SAN notation for moves everywhere
      - NTN_COORD - use coordinate notation everywhere
      - NTN_MIX   - use a mix of SAN and COORD, ie. Sloppy's current defaults
    - Don't read the game log when writing to game.pgn. Instead backtrack to the
      beginning and play the moves again.
    - Add (static) function prototypes at the beginning of each source file.
    - Don't try a null move if the side to move doesn't have any sliders.
      UPDATE: this took away a lot of strength, can't use it.
    - In Linux/Unix the default data folder is ~/.sloppy/ and in Windows it's
      the same folder where the executable is. User should also be able to
      choose the folder by running sloppy with -f <path> parameter.
    - Always completing the search iteration after the first root move takes
      about 5 - 8 % of the total search time, which is 5.3 - 8.7 % of the
      allocated time. So cut about 7 % out of the allocated time.
    - Use Verified Null-Move Pruning
    - Extend 3 plies when the search transitions into a pawn endgame
    - Generate (QUEEN) promotions in gen_qs_moves()
    - Try storing 2 best moves in transposition table
    - Order losing captures last
    - Store 2 positions in each hash entry: always replace and depth preferred
    - Try late move reductions in pv nodes


TODO:

    - gen_pc_moves() should be able to work with a const board pointer
    - Don't search the book if we're past X plies
    - Don't respond to ping while searching, unless in analyze/pondering mode
    - Support "avoid move" test positions
    - Implement pondering mode
    - If there's only one book move available and it has a score of 0, try to
      avoid choosing that move in search.
    - Use some more advanced source control system
    - Try the hash move boldly without any validation (move generation).
    - King safety extensions: extend all moves that significantly increase
      pressure against the enemy king.
    - Write a is_stalemate() function that can be called in sq_search() when
      gen_qs_moves() creates 0 moves.
    - Dismiss moves with a bad SEE value already in gen_qs_moves()
    - Carefully test all the commands in input.c and xboard.c
    - En passant captures should be handled in a cleaner way in move generation.
      The use of ep_sq should be consistent. In <Board> it's the <to> square,
      and in <Move> it's the square of the enemy pawn.
    - Optimize or get rid of get_threat_mask(), at least for generating legal
      king moves.
    - Search all captures in QS (ignore SEE) if a double check or
      discovered check is possible.
    - Add support for the UCI protocol
    - Special evals for endgames like KBNK
    - Detect blockades in eval
    - Get pointer arguments as constants if they're for reading only
    - In make_move(): if the move captures a rook, make sure the opponent
      loses castling rights in that corner. It's very unlikely that the other
      rook would later move there without the king moving first, but
      it's possible.
    - Get rid of EPD test support. There are better ways to run the test suites
      than having the engine support them.
    - Order the root moves more carefully, perhaps based on the node counts of
      previous searches.
    - Write more sophisticated wrappers for the platform-dependent dynamic
      library functions.