* fixes#3, removing override, adding clear documentation and changing api name
* adding Item.AddDuration, adding test coverage
* bumping version to 1.3.0
* added Podcast.AddPubDate() and Podcast.AddLastBuildDate() overrides.
* added Item.AddImage() to mask some cumbersome addition of IImage.
* added Item.AddPubDate to simply datetime setters.
* added more examples (mostly around Item struct).