Add alternative file format like 'sgf'

[Joker2770]

Is your feature request related to a problem? Please describe. A clear and concise description of what the problem is. Ex. I'm always frustrated when [...] Once I noticed that Sanmill saving game to file with txt format, and maybe there is a better or alternative way like sgf('Smart Game Format').

Describe the solution you'd like A clear and concise description of what you want to happen. With sgf format, the 'GM[5]' property is good for mill game. Then I found a good library named libsgfcplusplus. I think it is a good parser and builder for sgf files.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered. I think this feature will benefit for the promotion of Sanmill.

Additional context Add any other context or screenshots about the feature request here. reference

• sgf properties.
• sgf4.