雑なフォーマットにするならiso 8601って言っとくべきなんかな
> Why isn't this named `parse_from_iso8601`? That's because ISO 8601 allows some freedom over the syntax and RFC 3339 exercises that freedom to rigidly define a fixed format.
https://docs.rs/chrono/0.4.15/chrono/struct.DateTime.html#method.parse_from_rfc3339