Provide TimeSpan for expiry property of IDocument

The current expiry property for IDocument implementations is a uint which only allows for 49 days. The overloads that take a k/v pair offers a TimeSpan which allows for unlimited limit of days to expire. This ticket is to add an additional property to IDocument for a TimeStamp or change the Type from uint to ulong; changing the Type is a breaking change however should only be released as a major.