Bug: '00' is erroneously matched for months and days in date and date-time validation regexes

[RulerOfTheQueendom]

The regexes for both FormatOfStringDate and FormatOfStringDateTime in schema_formats.go allow 00 as a valid value for both months and days. This is explicitly specified by section 5.6 the RFC3339 standard as an out-of-range value.

Both regexes should be updated to disallow 00 as a valid value for months and days. Docs should be appropriately updated, and tests should be written as a stopgap measure against regressions.