Attribute parsing in SP of SAML response doesn't support FriendlyName or multiple values

[j00bar]

Howdy!

Happy to contribute a PR to support this, but it seems like the ResponseParser.attributes property could be improved in two ways:

1. If the SAML Attribute has a FriendlyName, it should be preferred over the Name - otherwise you get things like urn:oid:2.5.4.42 as a key versus givenName.
2. If there are multiple Attribute elements with the same name, only the first one appears in the attributes property, whereas some SAML assertions include multiple Role attributes.

Thanks!