Cleaned up XmlSitemapFeed facade members and changed the constructors of the specialized content factories to use the corresponding prepared content factory by default.
Made the IXmlSitemapUrlResolver into a formalized extension point by adding a IXmlSitemapUrlResolver factory. Factored out ISpecializedContentWriter from XmlSitemapWriter because there were issues with shared dependencies that caused tight coupling.
Created additional fluent builders for XmlSitemap configuration API.