Some go servers mistakenly generate sgf files without correct CA
properties. Use chardet to detect first 300 bytes.
Signed-off-by: Carton He <cartonhe@gmail.com>
For board <= 19x19, according to https://www.red-bean.com/sgf/go.html:
A pass move is shown as '[]' or alternatively as '[tt]' (only for boards
<= 19x19).
Carton He