Revision history for Game-Backgammon

0.01
    - Phase 01: the board, the position, the move, the turn and the
      notation. No play yet: the dice and legal turn generation are
      phase 02 and the rules are phase 03.
    - The position is one signed array read through Board::index_for, so
      exactly one class knows which way round the board is. t/03 greps the
      tree to keep it that way.
    - Phase 02: the dice, and the legal turn. Rolls are a pure function of
      the seed and the roll's number, hashed per roll so the seed proves the
      past and predicts nothing. The opening roll is really rolled.
    - legal_turns enumerates every sequence and then filters the set: both
      dice if any sequence plays both, the larger if only one can be, four
      on doubles, and the bar before anything else. A forfeit is a turn.
    - Phase 03: the game. play() takes a turn or its notation and matches it
      against the legal ones by the multiset of moves, so a turn the rules
      did not offer cannot be played whatever it claims. Hitting, the bar,
      bearing off (exact, higher-from-the-highest, and neither), the margin
      (single, gammon, backgammon) and finishing from outside.
    - Refusals are RETURNED as Game::Backgammon::Error, never thrown; die is
      for programmer error only.
    - Phase 04: the bot. One ply over the legal turns, scoring pip
      advantage, checkers off and on the bar, made points, the longest
      prime, an anchor, and blot exposure. Bounded in work and never in a
      clock, so it is safe inside a transaction: measured at 206 legal
      turns and 40ms in the worst position seen.
    - Phase 05: the terminal game draws a board rather than a list of
      numbers: both halves between their borders, the bar down the middle,
      the tray on the right, a point taller than five showing its count,
      round checkers with an --ascii fallback, and colour off a pipe. It is
      numbered from the side on roll, because a turn is written in the
      mover's own numbers; --view pins it. The legal turns are laid out
      across the screen instead of down it, and the screen is cleared
      between turns only for a person.
    - Game::Backgammon::Shots computes the hit-probability table by
      enumerating the 36 rolls, so the published shot table is a test of it
      rather than its source.