@pchote I need DateTime serialization in my replay-meta branch. See https://github.com/pavlos256/OpenRA/commit/bb20911c4faff9235dc5f9c05d9254d88a2f4d2c

I tought DateTimes will only be values, not keys, and didn't know they could cause problems for the parser. Since this PR adds DateTime serialization too, should I remove or change my implementation?