Floating implementation loop requires duplicate definitions in schema

[MikeEdgar]

When a loop implementation may occur in multiple locations (e.g. loop 2300 in common 837 implementation occurs in both loop 2000B and loop 2000C), the user is required to duplicate the full loop's definition within each of the locations in may occur. It would be better to allow for the loop to be declared outside of the <implementation> structure and be referenced at each point it is used.