fix -Wreorder
Merge pull request #45 from toxeus/fixReorder

fix -Wreorder
CMake: use -isystem for 3rd-party includes

That way we can increase the warning level without being affected
by the warnings that 3rd-party includes emit.
fix -Wcomment
Merge pull request #46 from toxeus/fixWarnings

Fix comment warnings
Remove ZMQ2, split ZMQ4 code / class in own files
Merge pull request #47 from lclc/zmq2remove

Remove ZMQ2, split ZMQ4 code / class in own files