Add support for calendar time

[evanstoner]

This is another Moment display function, similar to fromNow().

http://momentjs.com/docs/#/displaying/calendar-time/

[bschnelle]

+1

[Amareis]

+1. It's very good function and it must be supported, IMHO.

[jasonmit]

My newest PR (#139) will make adding new features like this easier through composition. Just waiting on @stefanpenner for a review and then will follow up with a PR to close this out.

[jasonmit]

Versioned as 5.1.0, I will create a separate issue for adding the computed property macro for it