New version of testcase document

A new version of the testcase doc is online at:

http://www.w3.org/2007/xmlsec/interop/xmlsig-interop-doc/testcases.html

The following changes were made in preparation for W3C Note:

Removed stale references that were not referenced.
Added reference for previous interop tests doc.
Removed Document History section.
Added contributors list.
Removed notes for additional editors.
Reviewed all hyperlinks.
Used the term "Test Cases" consistently throughout doc.


I believe the only change left is to change the shortname to 
"xmldsiged2-tests"

Please review and let me know if it looks ok.

--Sean