threads dependency required to link with core

ocaml-openflow links against core, hence this module does so too
removed ocamldoc configuration
handcrafted Makefile

Even though topology has no submodules, this handcrafted file cleans up
setup.data, which is a win.
handcrafted Makefile removes setup.data
Merge pull request #21 from frenetic-lang/final-async

core/async compatibility and better makefiles