saml2 2.1.0

The saml2 library is yet another SAML library for Ruby, with an emphasis on _not_ re-implementing XML, especially XML Security, _not_ parsing via Regex or generating XML by string concatenation, _not_ serializing/re-parsing multiple times just to get it into the correct format to sign or validate. For now, it provides a clean interface for implementing an IdP, but not an SP.