XML\md\EntityDescriptor to Configuration\EntityIdProvider conversion

[johnorourke]

Hi, I'm using this library without simplesamlphp, to implement deep inspection of SAML in a proxy. I'd like to make use of SAML2\Response\Processor using metadata, which means writing my own converter to build SAML2\Configuration* objects from XML\md* objects. Would this be of interest to the community? If so I'll try to write as part of the library and submit a pull req.