SGF for large board sizes

[tasuki]

• LittleGolem uses a-z for the coords and then just goes on and on. Parse by doing i - 96
• https://www.red-bean.com/sgf/go.html says: "In FF[4] it is possible to specify board sizes upto 52x52. In this case uppercase letters are used to represent points from 27-52, i.e. 'a'=1 ... 'z'=26 , 'A'=27 ... 'Z'=52"
• https://www.red-bean.com/sgf/twixt.html says: "If more than 26 columns are used, then the form letter letter number is used. After Z comes AA, then AB, AC, etc."
• https://www.red-bean.com/sgf/hex.html says: "If there are more than 26 columns, they are identified by base-26 alphabet numbers, i.e., the next columns after z are aa, ab, ac, ..., az, ba, bb, and so on. The next column after zz is aaa."

But I don't want to implement different handling for different games, so I guess LG notation it is?