remove signature element for a log out request

SAML 2.0 spec requires the signature element be removed from
the request body.  This commit removes the signature in the body.

See lines 578-579 in http://docs.oasis-open.org/security/saml/v2.0/saml-bindings-2.0-os.pdf
Merge pull request #20 from ncloward/original_version

remove signature element for a log out request
bump version to 0.1.26 to match rubygems.org
Merge pull request #21 from ncloward/original_version

bump version to 0.1.26 to match rubygems.org
don't add newlines to the base64 encoded data
bump version to 0.1.27