Copy of System.ServiceModel.Syndication

Copy from https://github.com/mono/mono/tree/master/mcs/class/System.ServiceModel.Web/System.ServiceModel.Syndication

and slightly modified to compile standalone

Signed-off-by: Emmanuel Mathot <emmanuel.mahot@gmail.com>
solution and ignore

Signed-off-by: Emmanuel Mathot <emmanuel.mahot@gmail.com>
ignore

Signed-off-by: Emmanuel Mathot <emmanuel.mahot@gmail.com>