Added TestBase class and updated tests
Added SitemapNamespaceConstants for define image,video etc like namespaces
Added ImageDefinition for  supporting image sitemaps
Changed serialization logic from System.Runtime.Serialization to System.Xml.Serialization
Updated XmlSerializer to use System.Xml.Serialization techniques
Added new method to SitemapProvider for creating sitemapindex
Added sample project and configured assembly binding redirects
Implemented code highlighting for sample codes
Update README.md
Created IXmlNamespaceResolver for provide necessary namespace declarations for xmlserializer
Matched class and file name
Implemented ShouldSerialize* pattern for handling nullable properties
Fixed forgotten comment
Update README.md
Code refactoring
Deleted OutputCache attribute definitions
Added Serialize_SitemapNodeWithImageDefinition test
Renamed SitemapNamespaceConstants class
Removed xmlns:i
Formatting