Add a relaxed datetime parser. This datetime parser functions by using `chrono`sown parsing utilities and a try/succeed approach to parsing.This implementation of the datetime parser has some drawbacks and somepositives. On the positive side:- it was easy to implement- it is easy to add more datetime formats toIn order to add additionally supported formats, a developer can add therequired format string to the `format` mod in `parse_datetime.rs`, andthen add it as a potential format to the relevant `fmts` vec.On the negative:- It is not easily customiseable beyond the supported `chrono` parsing  formats. E.g., `chrono` does not currently support parsing offsets  without trailing zeros. `from_str("UTC+1")` should return a valid response  but `chrono` fails to parse this.- Because it is an attempt driven parser, it is likely not that  performant. I have not done any performance testing as part of thischange, but I would expect a custom parser to perform much better.

Co-authored-by: Sylvestre Ledru <sledru@mozilla.com>

Update the README and add a test module to parse_datetime for anyexamples presented in the README.

add datetime parser

Also fuzz fuzz_parse_datetime_from_str for a minute

rename from humantime_to_duration to parse_datetime