Also calculate time to go

[chandrashan]

Currently designed to calculate how long ago something was.

I have modified it to a formatTimeUntil() function which just swaps the timestamp around and gives the time until.

Could either have two functions - formatTimeUntil() and formatTimeAgo(), or get clever and combine the two into one function automatically. Am relatively new to Dart - but perhaps by taking the 'absolute' value then it should be pretty easy to keep things consistent?

if I work out how to add a pull request I'll submit...

[chandrashan]

submitted pull request #3 which adds in this functionality and for issue #1