Added upgrade implementation for other pieces.

.godot/editor/editor_layout.cfg

.godot/editor/filesystem_cache8

.godot/editor/filesystem_update4

.godot/editor/script_editor_cache.cfg

scripts/Assassin.gd

scripts/Bishop.gd

scripts/King.gd

scripts/Knight.gd

scripts/Mage.gd

scripts/Pawn.gd

scripts/Queen.gd

scripts/Rook.gd

scripts/Shop.gd

scripts/Upgrade.gd

scripts/Wizard.gd

scripts/game.gd