--enable-tests --enable-quickcheck tweak

--enable-tests *always* builds the test suite and openflow.quickcheck,
which the tests require

--enable-quickcheck builds openflow.quickcheck, but not the test suite
removed ocamldoc configuration from _oasis

opam-doc, chaps
removed _oasis generated ./configure and Makefile
better, hand-crafted Makefile

Based on the Cstruct Makefile:

https://github.com/avsm/ocaml-cstruct/blob/master/Makefile

Key features:

- "make clean" deletes setup.data, which is generated by configure
- make builds the async submodule if async is installed (and similarly for
  lwt and quickcheck)