ISSUE 62: Versioning

As I promised, here is a proposal including exact word changes

At line 619 (of version 13, after the paragraph describing
/wsse:SecurityTokenReference/@wsse:Usage)
add

/wsse:SecurityTokenReference/@Version

This optional attribute indicates what profile and version provides
the semantics of this SecurityTokenReference. It is a URN specified in
some profile.  For example, the identifier for version 1 of the X509
profile might be
"urn:oasis:names:tc:WSS:1.0:profiles:WSS-X509"

Corresponding change to the .xsd (my xsd knowledge is almost
non-existent so this may be wrong) 

add

<xsd:attribute name="Version"
type="xsd:anyURI"/>

to the definition of SecurityTokenReferenceType
If the above is accepted, then the editors of all profiles will need
to ensure that a URI is specified in that profile and I hope they could
agree on some uniform scheme.