(1) Add a bunch of tedious type casts to eliminate unnecessary compiler warnings on Windows X64 builds.
(2) Some EthernetTap work to integrate Windows custom IOCTL for multicast group lookup (not done quite yet).
(3) Dump some more info in selftest to make sure our Windows path lookup functions are returning sane results.
(1) Probable fix for issue #7 and major cleanup of EthernetTap code with consolidation for all unix-like systems and specialization for different flavors only when needed.
(2) Refactor of Buffer<> to make its members private, and Packet to use Buffer's methods exclusively to access them. This improves clarity and means we're no longer lying about Buffer's role in the code's security posture.
(3) Add -fstack-protect to Makefile to bounds check stack variables.
