#359 - no longer requiring Now when raising events

Fixes #359.

Includes functionality that had been discussed as an add-on to #30 (and will enable changes for that issue).
`TryTakeArgumentProviderFor`? Inspired by [`ConcurrentBag<T>.TryTake`](http://msdn.microsoft.com/en-GB/library/dd381774(v=vs.100).aspx)?