Small modification to the attribute graph
Use a target specific variable for a target's object files:

* This eliminates the need to filter based on SCAFFOD_OBJ_SUFFIX.
  This is in preparation for a objs attribute.
Add support for the objs attribute:

* This attribute is used to specify pre-compiled object files that
  make up a binary.
New module_rules attribute:

* This attribute allows the specification of a makefile to include for
  supplemental rules.  This is done so that all the targets in a
  module.mk will also depend on the rules makefiles.

* This replaces the static module-rules.mk file.