Change the piece order again

Change the piece order again

The internal piece encoding is now altered such that the uninteresting
ones (promoted Shogi pieces and symmetry partners) are all at the end,
just before King. These now start with the PromoBishop. A slash in the
pieceToChar string skips to this new 'promoted series', so that strings
can be made 'future proof' (for when new pieces are added before it).
The promoted Chu pieces all get new book keys by this, but as it is
unlikely that they occurin opening lines, this was considered acceptable.
The +L, +T in Chu are now represented by Pegasus and Gnu rather than
Knight and Chancellor, but the latter two are defined as fall-backs to
remain compatible with old Chu themes.
The +N, +L, +S replacements in Shogi are now also taken from amongst the
regular pieces, rather than extra images stored beyond King.