Adds prefixing to Assertion elements.
Adds prefix to SAMLResponseXmlSigner.
Changes Issuer to be a string instead of a URI.
Changes Audiences from URI[] to string[]

-While integrating with some sites, we have found that the SAML2.0
 spec is not always followed. So instead of making sure that the spec
 is followed we are putting the onus on the SamlResponseHandler to ensure
 that the Response adheres to whatever format is expected for that
 particular client.
Merge pull request #22 from sbartlett/master

Adds some changes to how we parse/create SAML Responses.