All algorithms now compile with the utils in utils/, they all use the
same interface.h.

In this change:
- removed local copies of interface.h.
- updated interface.h to really be the same for all.
- added extern "C" and proper includes so .cpp would compile.
- tweaked Makefiles to allow for inclusion of interface.h and
  the ds_ssort files in a uniform way.
- added a global makefile to cleanup all algorithms/.