These are instructions for adding a new primitive operator to the IL.

  1) add it to the spec files in compiler/gen/il and run gen.sh

  2) add rules for generating the type signature in the appropriate checking modules in
	high-il/check-high-il.sml
	mid-il/check-mid-il.sml
	low-il/check-low-il.sml

  3) add rules to translate the operator between ILs in
	high-to-mid/high-to-mid.sml
	mid-to-low/mid-to-low.sml

  4) add code generation support