Add support for SAML 1 Tokens

This pull requests add support for SAML 1 Tokens. There are a couple things to note:

* I based the saml1_example.xml on the service I am communicating with, but replaced most of the values with the corresponding values in acs_example.xml
* Your comments in auth_callback.rb imply that you did not expect "audience" to vary between SAML 1 and SAML 2. I needed these to differ because SAML 1 has namespaces attached to the elements.
* I needed to make a change to xml_security.rb because the ID in the "check digests" section is named "AssertionID" instead of "ID".

Let me know if you have any feedback about how this could be improved. Thanks.
I think that checking both would be the fastest way to solve this

```ruby
hashed_element = \
  REXML::XPath.first(self, "//[@ID='#{uri[1,uri.size]}']") ||
  REXML::XPath.first(self, "//[@AssertionID='#{uri[1,uri.size]}']")
```