add NP::IPX
tweaks and cleanups
Merge branch 'ipx'
NP::Ethernet now support 'encode'
Merge branch 'ethernet-encoding'
v1.5.0

 [ENHANCEMENTS]
 - Addition of NetPacket::IPX. (Daniel Collins)
 - NetPacket::Ethernet implements 'encode'. (RT#93928, Guido Hungerbuehler)

 [STATISTICS]
 - code churn: 7 files changed, 337 insertions(+), 13 deletions(-)