Replace SimpleSAML_Auth_* with namespaced version

docs/simplesamlphp-authproc.md

docs/simplesamlphp-authsource.md

docs/simplesamlphp-errorhandling.md

docs/simplesamlphp-sp-api.md

lib/SimpleSAML/Auth/Default.php

lib/SimpleSAML/Auth/LDAP.php

lib/SimpleSAML/Auth/ProcessingChain.php

lib/SimpleSAML/Auth/ProcessingFilter.php

lib/SimpleSAML/Auth/Simple.php

lib/SimpleSAML/Auth/Source.php

lib/SimpleSAML/Auth/SourceFactory.php

lib/SimpleSAML/Auth/State.php

lib/SimpleSAML/Auth/TimeLimitedToken.php

lib/SimpleSAML/AuthMemCookie.php

lib/SimpleSAML/Error/UnserializableException.php

lib/SimpleSAML/IdP.php

lib/SimpleSAML/IdP/IFrameLogoutHandler.php

lib/SimpleSAML/IdP/TraditionalLogoutHandler.php

lib/SimpleSAML/Utilities.php

lib/SimpleSAML/Utils/Auth.php