add amd module definition pattern

[sechel]

Hi nice work, I added amd module definition. By the way, from the Docs, this does not work in Browsers var d = Duration.parse("5h"), now = new Date(), later = new Date(now + d); console.log(later.toString()); need to use Date.now() + d

[icholy]

If you want this merged, please remove the changes in toString.

[sechel]

done, sorry I pulled in this toString extension from somewhere else.