Use RFC3339 timestamps

[mattaezell]

RFC3339 implements ISO8601. "It is a conformant subset of the ISO 8601 extended format. Simplicity is achieved by making most fields and punctuation mandatory."
partial-issue: #19

[mattaezell]

Note: golang also has a time.RFC3339Nano, but it uses .999999999 for the fraction of seconds which will trim zeros at the end. Instead we use .000000000

[chenglch]

Thanks