Corrected link to [Jackson04] paper.
Added 'discrete' enumeration selection to 'interpolate' attribute of <independentVarPts> and
<independentVarRef>
elements at the suggestion of Geoff Brian, DSTO.
Added section and <variableDef> example on extending the MathML 2 function set
with atan2
Removed all xns attributes from examples
Amplified that it is a good practice to provide <variableDef>s in sorted
sequence