Linux TUN device support
Pull
Device.h: added bool Device::send(const std::string&)
IPv6.{h,cpp}: IPv6 packet bit-twiddling and reconstruction namespace
TUNDevice handles reads through libev, NAT dropped from IPv6::Packet
CryptoIdentity::our_businesscard: compute only once
CryptoIdentity::CryptoIdentity: fix last commit: allocate object
TUNDevice::read_cb: read is now MTU independent; buildsystem now requires LEMON, compiling against internal nacl works
Internal nacl lacks C++ glue code, removing
TUNDevice::TUNDevice: correct IPv6 address
asserts in IPv6, rename TUN, remove deprecated functions
TUNInterface: Hide file descriptor
FindNACL.cmake: cleanup; FindLEMON.cmake: license text
Merge pull request #1 from andreasots/master

Linux TUN device and some more fixes