Preview a chess position when hovering above a valid FEN string

based on FEN viewer by asimos-bot

This extension contributes the following settings:

• fenlense.showCastlingRights: Show indicators for who can castle and in wich direction
• fenlense.showEnpassantSquare: Show Indicatetor for En Passant target square
• fenlense.lightSquareColor: Color of light squares as RGB hex color code
• fenlense.darkSquareColor: Color of dark squares as RGB hex color code
• fenlense.castlingRightsColor: Color of castling rights indicators as RGB hex color code
• fenlense.enPassantSquareColor: Color of En Passant square indicator as RGB hex color code