Added missing duration unit short names that are supported in scala and more

Added missing duration unit short names that are supported in scala.concurrent.duration.DurationConversions, namely nano, nanos, micro, micros, milli and millis.

Also added a few more shorthands for hours, minutes and seconds, hr, hrs, min, mins, sec and secs. I'll revert the addition of these extra shorthands if people are not happy with them.