Add new port devel/py-strict-rfc3339: Strict, simple, lightweight RFC3339 functions

Simple and lightweight python module to validate, parse and generate RFC3339
time strings. It was initially created as a part of habitat in response to
difficulty using other libraries.

It can convert UNIX timestamps to and from RFC3339, either producing strings
with a UTC offset (Z) or with the offset that the C time module reports is
the local timezone offset. It has minimal dependencies (none beyond those
that come with Python) and avoids the error-prone act of dealing with
timezones as much as possible.

Besides that, it's designed to be strict and stick closely to RFC3339, with a
couple of very small caveats. It's also fully unit tested.

WWW: http://www.danielrichman.co.uk/libraries/strict-rfc3339.html

PR: 227031
Submitted by: Kai <freebsd_ports@k-worx.org>