Add dateTime Format

[jinglesthula]

Currently it supports relativeTime and authorTime in the Format setting. relativeTime looks like it's the number of seconds since the commit. It would be great if that could be formatted as a datetime value (yyyy-mm-dd hh:mm:ss), or if the current way it's doing it needs to be maintained, to provide an additional dateTime format token that would apply the formatting (perhaps with moment.js).

This would really help if you have 2 lines where they both say "about a year ago" with relativeTime, and the number of seconds is a bit difficult to compare visually.

Very useful package, by the way. Thanks!