fix for inconsistent c strftime implementations

[drewbanin]

This PR tweaks the implementation of strftime to:

• try using the Singer strftime implementation
• fall back to an alternative date fmt string: %Y-%m-%dT%H:%M:%S.%fZ

As a result, tap-codat should now work on any system regardless of the underlying C strftime implementation

[KAllan357]

:+1: