add Hello module:
 - handling of bitmap version message
 - the roundtrip test is very basic since it cause some trouble in some generation
modify the test for VersionBitmap in order to be a bit more complete
Merge branch 'barrier' of https://github.com/fugitifduck/ocaml-openflow into helloMsg
Merge branch 'helloMsg' of https://github.com/fugitifduck/ocaml-openflow into helloMsg
Merge remote-tracking branch 'upstream/master' into helloMsg
Merge branch 'master' of https://github.com/frenetic-lang/ocaml-openflow into helloMsg
use type t in function
Merge branch 'master' into helloMsg

solve Conflicts in:
	lib/OpenFlow0x04.ml
	lib/OpenFlow0x04.mli
	lib/OpenFlow0x04_Core.ml
	lib/OpenFlow0x04_Core.mli
	quickcheck/Arbitrary_OpenFlow0x04.ml
	test/Test.ml
generate arbitrary list (and null list) for hello element
Merge branch 'barrier' into helloMsg

Conflicts:
	lib/OpenFlow0x04.ml
Arbitrary unique sorted list for bitmap version in hello element.

the value of 300 is made to minimise the running time of the marshing function (and the parsing).
Merge pull request #137 from fugitifduck/helloMsg

Hello msg