* begin adding better fuzz test
* finish adding working fuzzer
* implement mutateipv4
* fuzzer finds a panic in ICMP client on receive empty payload
* rename fuzz tests to reflect fuzz methodology
* begin adding icmp client
* rely on anon structs
* add tests
* tests passing
* icmp fleshed out
* rework icmp to include ip addr
* rename StackAsync.Demux/Encapsulate to RecvEthernet and SendEthernet
* remove legacy unreachable TCP tests
* remove uses of deprecated internet.StackNode in preference of lneto.StackNode
* documentation
* rename methods to signal no I/O happening