complete bucket module (to_string, parse)

groupType : add to_string and parse
and correct OFPGC -> OFPGT

add groupDesc module
add groupFeatures module
add MeterStats module
add meterfeaturesStats and add new types to multipartReply
complete groupMod module
change TableFeaturesRequest to TableFeature
add TableFeatureReply
complete meterBand module
move MeterFlags to a separate module
complete meterConfig module
add unitary test for missing multipartReply
Correct OXM TCP TLV (bug : no mask)

add missing OXM TLV:
  OxmUDPSrc
  OxmUDPDst
  OxmSCTPSrc
  OxmSCTPDst
  OxmIPv6Src
  OxmIPv6Dst
  OxmIPv6FLabel
  OxmICMPv6Type
  OxmICMPv6Code
  OxmIPv6NDTarget
  OxmIPv6NDSll
  OxmIPv6NDTll
  OxmMPLSBos
  OxmPBBIsid
  OxmIPv6ExtHdr
merge from master
add missing messags
add packetOut message
complete error messages
issue #131, oxm export its type
issue #131, PacketOut export its type
issue #131, MultipartMessages export its type
move function of GroupFeatures in submodule
move function of MeterFeaturesStats in submodule
move function of MeterStats in submodule
export type t and move function to submodule for more clarty
correct padding for bucket
change GroupDesc to basic type

add rountrip test for bucket and groupdesc
change MeterStats to basic type