Ability to parse an ISO Duration string

[redben]

Hi,
It would be nice if moment supported ISO duration format, like :
moment.duration("PT16H40M");

[mattjohnsonpint]

+1.

Also, you should be able to format a duration this way, or using other format specifiers such as:

moment.duration(3.25, 'minutes').format('mm:ss')

Probably duration#format without parameters would format as an ISO duration.

[ichernev]

We'd accept a pull request for parsing ISO duration tokens. About printing with a format -- that's been requested multiple times: #463, #704.

[icambron]

Closed by #1113