Strict, simple, lightweight RFC3339 functions

Goals
-----

 - Convert unix timestamps to and from RFC3339.
 - Either produce RFC3339 strings with a UTC offset (Z) or with the offset
   that the C time module reports is the local timezone offset.
 - Simple with minimal dependencies/libraries.
 - Avoid timezones as much as possible.
 - Be very strict and follow RFC3339.

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