Separated the create_authentication_xml_doc in two methods

[levelboy]

@pitbulk
I ran in a problem that I can't find a good solution for.
I want to be able to add Scoping namespaces as per @tekt8tket 's PR

I do understand your need to keep the library simple
I'm also thinking that the SAML standard is pretty big, and a library cannot cover all the usecases of SAML.
Because of this, I find it imperative that the library should be open for extension.
The way Authrequest.create_authentication_xml_doc is now, with the signing of the document before it's returned, doesn't even allow easy monkey patching.

So this is what I propose, a very simple split in the Authrequest.create_authentication_xml_doc between the creation and population of the document, and the signing, so you can hook your code between them.

What do you think?

[pitbulk]

I'm ok with this solution. Right now I'm working on implementing a new ruby-common-gem that will have the core functionalities (handle general SAML xmls, sign, validations, encryption, decryption) and the ruby-saml wil delegate on it all those functionality.
I will keep this in mind when releasing the new ruby-saml version.

[levelboy]

Ok @pitbulk, thank you