More DRY, uses splatting, added help, changed output type, updated README

[briantist]

I know these are some major changes, but I think they're useful.

The big breaking change is changing the output type to a [TimeSpan]. I think this is important; it's more versatile and contains more information. One can easily get the days out of the timespan returned, or use it directly for something that needs a timespan, but one cannot get the missing information if a number of days is returned.

[itadder]

Thanks for the update. and for adding help.
Briantist made some changes to my simple script, and updated the readme.

Thanks Briantist