Implementation of DateTime, TimeSpan and a couple of other things

Hi Zach,

As the title says, I implemented almost complete versions of DateTime and TimeSpan with working unit tests. I only had problems overriding the DateTime.ToString(), I opened an issue about the idem.

I also cleaned up a bit my previous implementation of Enumerators for imperative collections (ResizeArray, Dictionary, MatchCollection...) and exposed a couple of things which I need for the HTML extensions: Async.protectedCont and WebRequest.Url. I hope this is fine. 

Please have a look when you have time and tell me what you think.

Cheers!
Alfonso