Errors parsing dates

[radu-matei]

We've had a few distinct errors parsing the date field in the page header:

• for date = "2022-03-14":

TOML parsing error: input is not enough for unique date and time for key `date` at line 3 column 8

• for date = "2022-03-14T00:22:56Z" (on Windows, not exactly sure what the issue is here, the error is very NOT helpful):

`Error rendering "content_top" line 30, col 54: date_format helper: Couldn't convert parameter date to type DateTime < Utc >. It's Null as JSON. Got these params: [PathAndJson { relative_path: None, value: Constant(String("%Y-%m-%dT%H:%M:%SZ")) }, PathAndJson { relative_path: Some("page.head.date"), value: Context(Null, ["page", "head", "date"]) }]`

[technosophos]

the date parser is very strict. So it MUST be a full ISO 8601 date.

I have no idea what the problem with the second date is. I'm not even sure how there can be an error on Windows that doesn't appear on other OSes. AFAIK, the date parser does not use any host OS features.