[xacml] Functions Document

Okay, here is the current functions document.

From the last document, the changes we made are as follows:

We've removed xs:NOTATION functions, and the decimal-mod.
We removed "abs" and replaced it with:

integer-abs
decimal-abs

to be consistent.

We've removed first, rest, functions due to non-order preserving
evaluation schemes.

We've added the following functions for each primitve data type:

type-sequence
       which takes any number of arguments of the specified type
       (not sequences) and promotes it to a sequence<type>.

type-at-least-one-member-of
	which is the logical OR of applications of the type-member-of
        function between each element of the first argument and the
        second argument sequence.

type-set-equals
        which is the logical AND of the application of the type-subset
        function to the first and second arguments and to the second
        and first arguements