[xacml] Decimal Arithmetic Standard

I've found a specification document that outlines in an understandable
fashion the IEEE and ANSI and ITU standards for arithmetic and
number conversions.

http://www2.hursley.ibm.com/decimal/decarith.html

However, we still have to list a number of defaults for handling the
arithmetic, not only for the explict "round" operation, but especially for
"rounding" durning operations such as divide and "decimal-to-integer".

I gather we have not yet found a standard for Date arithmetic.

-Polar