Merge pull request #3 from dolfandringa/master

As requested by up_the_irons my contribution
get_assertion_attribute_value added to Response object. This method can retrieve AssertionAttributes from the assertion tag
added the required imports and fixed the typo
Merge pull request #4 from dolfandringa/master

Hey all, I have another addition: reading saml:Attribute tags
Merge pull request #7 from claytantor/master

Push to fix import and typo
Merge branch 'master' of http://www.github.com/dolfandringa/python-saml
Merge remote-tracking branch 'upstream/master'