[security-services] XML signature guidelines draft

Sorry this has taken so long, day job and all that.

It's in Word form, and I plugged it into the template used by the other
documents, feel free to do whatever is needed with that.

To avoid all the potential unpleasantness, I wrote this on my own time,
as an individual member of OASIS, and provide the entire text to the
technical committee to do with as they please, with no further claim on
it. Yadda, yadda.

-- Scott