Proposal: Adding a nanosecond resolution now()

[p-casgrain]

I think it would be useful to add a higher-resolution version of Dates.now(). Possible implementation could be something like

function now_μs()
    tv = Libc.TimeVal()
    tm = Libc.TmStruct(tv.sec)
    return TimeDate(tm.year + 1900, tm.month + 1, Int64(tm.mday), Int64(tm.hour), Int64(tm.min), Int64(tm.sec)) + Microsecond(tv.usec)
end

which gives the current date/time to the microsecond level.

This expression gives it up to nanosecond resolution but in GMT time zone.

now_ns() = TimeDate(1970) + Nanosecond(time()*1e9)

I am not sure how to get in the system timezone.

If this is fine, I can make a PR with this bit inside.

[JeffreySarnoff]

please do