New proposal for Requirements document - ACTION-73 completed

Based on Frederick's feedback on my earlier proposal for ACTION-73, this 
is my updated version, suggesting we can close this item (after wg review, 
of course).

-- Magnus
--
Title:
------
Change title from

XML Signature and Canonicalization: Requirements and Design Notes

to

XML Security Use Cases and Requirements

Scope/Content:
--------------
In order to have a consistent treatment of XML Enc as well as XML Sig and 
simplify the layout of the text, I suggest changing the current scope/content 
to:

1 Scope
2 Introduction
3 Principles
4 Usage scenarios
   4.1 XML signature
       (incl. canonicalization)
   4.2 XML encryption
5 XML Signature Design Requirements
  (to include canonicalization Design Requirements as already in the
   current Aug 20 draft)
    5.1 Fundamentals
    5.2 Design Options
    5.3 Requirements
6 XML Encryption Design Requirements
    6.1 Fundamentals
    6.2 Design Options
    6.3 Requirements
7 Acknowledgments
8 References