Switch from iso8601 to chrono #23
Description
It looks like the iso8601 crate is no longer actively maintained: badboy/iso8601#19
It would be good to switch to the chrono crate. This will help reduce the amount of unmaintained code floating around.
The major difference is that iso8601 has more flexible parsing (it tries to autodetect the format), whereas chrono wants you to specify the format up-front.
Arguably iso8601's "magic behaviour" of parsing is potentially surprising and not such a great thing anyways, but if really needed one could maybe implement it using chrono's primitives.