[ENHANCEMENT]: Improve experience of adding a `Reference` to the `Signature`.

[cjbarth]

Is your feature request related to a problem? Please describe...

By default, a Reference isn't added for all the first-level nodes in an XML document in the Signature block. This means that the <KeyInfo /> Reference isn't included in the Signature block.

Describe teh solution you'd like...

The default, or a simple function call, should be present to allow adding Reference elements for all parts of the document being signed.

You can see more about someone trying to do this with C# here.

Describe the alternatives you've considered...

Adding a Reference to each part of the document to be signed is cumbersome and still leaves <KeyInfo /> without a Reference.