Add constants for Unicode symbols
user
```ruby
module Chess
    W_KING   = "\u2654"
    W_QUEEN  = "\u2655"
    W_ROOK   = "\u2656"
    W_BISHOP = "\u2657"
    W_KNIGHT = "\u2658"
    W_PAWN   = "\u2659"
    B_KING   = "\u265A"
    B_QUEEN  = "\u265B"
    B_ROOK   = "\u265C"
    B_BISHOP = "\u265D"
    B_KNIGHT = "\u265E"
    B_PAWN   = "\u265F"
end
```
assistant