Add VariableDefinitions as optional elements in PolicySet (like in Policy) with local scope only [OBSOLETED by #11 in XACML 4.0]

[cdanger]

This is obsoleted by #11 in XACML 4.0.

Add the possibility to have VariableDefinitions in PolicySets (like in Policies) as optional elements.

See also #3 for similar request on Rules.

In this feature request, the variables scope is limited to the embedded/inline Policies (not extended to referenced policies). This change would be backward compatible.

For a similar feature request but enhanced with variables scope extended to referenced policies, although more complex and possibly breaking backward compatibility, see issue #4 .

[cdanger]

Closing... in favor of #11 .