Modified Makefile to not require ocamlfind or netstring
and created a slice of json_io.ml  in json_out.ml.

Json-wheel is better structured than sexplib. Martin correctly
realized that people may want to use Json as-is, without the automatic
converting camlp4 stuff. So he splitted in json-wheel and json-static.
They should have done that for sexplib too. Nevertheless he requires
netconversion stuff :(