Add a game state log dumping facility that produces a (load)able sexpr-log.

[eow] / testdata / xdump-meta-meta.txt

XDUMP meta meta 1242293190
"name" 3 4 0 -1
"type" 4 4 0 34
"flags" 5 12 0 33
"len" 7 4 0 -1
"table" 8 4 0 -1
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