python-chess v0.3.0

New in this release:

• Rename property half_moves of Bitboard to halfmove_clock.

• Rename property ply of Bitboard to fullmove_number.

• Let PGN parser handle symbols like !, ?, !? and so on by converting
  them to NAGs.

• Add a human readable string representation for Bitboards.

  >>> print(chess.Bitboard())
  r n b q k b n r
  p p p p p p p p
  . . . . . . . .
  . . . . . . . .
  . . . . . . . .
  . . . . . . . .
  P P P P P P P P
  R N B Q K B N R
  

• Various documentation improvements.