Compatibility with Microsoft ADFS 2.0

Added a short Read Me text file with steps to follow in order to use
PAC4J against ADFS.
Modified SAML2 response validation. NameID is not needed if at least one
Subject Confirmation is present (even without a NameID). BaseID is also
accepted. If NameID is empty, a dummy NameID is used for SAML2
credentials.
I would prefer to build the fake nameID at the end of the Saml2ResponseValidator. By the way, I think we should not transform an attribute in nameID, it is the application responsibility to consume the assertion as it is.