SBVR_ — ‘expression’ as a bindable target

Have any expression be a bindable target, rather than just a text. Note the referent of the binding is the expression itself, not a meaning of the expression. The reason the initial SBVR submission was limited to ‘text’ is that only ‘text’ expressions occur in XMI. But other sorts of expressions should work just fine if a reference scheme is used.

Change the definition of bindable target to use 'expression' in place of 'text' and add notes to explain the interpretation of a bindable target.