Add support for RFC3339Nano as another zapcore.TimeEncoder

[nattawitc]

zapcore package has implemented 4 types of TimeEncoder (Epoch, EpochMillis, EpochNanos, and ISO8601). Is it possible to add RFC3339 and RFC3339Nano or any other standard format in go's time package. I've seen this implemented in #276 , but I couldn't find it anymore in the current version.

Another solution is to implement a custom TimeEncoder ourself

func rfc3339TimeEncoder(t time.Time, enc zapcore.PrimitiveArrayEncoder) { enc.AppendString(t.Format(time.RFC3339Nano)) }

but I'm not sure if it will cause any further issues as TimeEncoder.UnmarshalText does not support custom one.

[NathanZook]

I'm pretty sure that that is only used for zap.Config#Build. BTW, RFC3339Nano especially is ill-behaved. Here's what I'm using:

func Iso3339CleanTime(t time) string {
        t.UTC().Format("2006-01-02T15:04:05.000000Z")
}

func Iso3339CleanTimeEncoder(t time.Time, enc zapcore.PrimitiveArrayEncoder) {
        enc.AppendString(Iso3339CleanTime(t))
}