It would be nice if there was a separate config option for `inputFormat` separate to the display `format` as Moment accepts an array of input formats as the second param to allow for multiple input formats eg ['YYYY-MM-DD', 'MM-DD-YYYY', 'DD-MM-YYYY'].  This option would default to the display format if not provided.  

I bring this up as I'm wanting this feature now, and user's who may want to provide custom date formatter functions may well want to provide a custom date parser function as well.  This would be the place to allow for a custom date string parser.