Patch to register XmlSyntax and RegularPatterns as known extensions

Hi all, I'd like to have concrete XML syntax (HSP) and regular expression pattern syntax (HaRP) registered in Language.Haskell.Extension. The attached patch registers XmlSyntax and RegularPatterns as constructors in the Language.Haskell.Extension.Extension data type, along with haddock documentation. Cheers, /Niklas