Return duration as property on time object

[macandcheese]

Hi there, thanks for this package!

I'm having some trouble accessing the resultant "duration" of two dates as a property.

Take for example <Moment duration={date.startTime} date={date.endTime} />

This will correctly print the expected duration in a template, but doesn't make that value available as a property, since "duration" is already used for the startTime.

I would expect the syntax to be more along the lines of something like:

<Moment durationStart={date.startTime} durationEnd={date.endTime} />

and then have the result, myDate.props.duration available on the object.

Maybe I'm just missing something?