libzmq: update to version 4.3.1

lib/zmq/README.md

@@ -0,0 +1,57 @@
+# Build libzmq for Zebus
+
+Download the latest release of [libzmq](https://github.com/zeromq/libzmq/releases) and extract it.
+
+## Windows
+
+Open a *Developer Command Prompt for VS 2017* inside the source directory.
+
+### x64
+
+```
+mkdir build_x64
+cd build_x64
+cmake -G "Visual Studio 15 2017 Win64" -D WITH_PERF_TOOL=OFF -D ZMQ_BUILD_TESTS=OFF -D ENABLE_CPACK=OFF -D CMAKE_BUILD_TYPE=Release ..
+msbuild /m /v:m /p:Configuration=Release /p:Platform=x64 ZeroMQ.sln
+```
+
+The dynamic library will be outputted in `bin\Release\libzmq-*.dll`.
+
+### x86
+
+```
+mkdir build_x86
+cd build_x86
+cmake -G "Visual Studio 15 2017" -D WITH_PERF_TOOL=OFF -D ZMQ_BUILD_TESTS=OFF -D ENABLE_CPACK=OFF -D CMAKE_BUILD_TYPE=Release ..
+msbuild /m /v:m /p:Configuration=Release /p:Platform=Win32 ZeroMQ.sln
+```
+
+The dynamic library will be outputted in `bin\Release\libzmq-*.dll`.
+
+## GNU+Linux
+
+Open a shell inside the source directory.
+
+### amd64
+
+```
+mkdir build_amd64
+cd build_amd64
+cmake -DWITH_PERF_TOOL=OFF -DZMQ_BUILD_TESTS=OFF -DCMAKE_BUILD_TYPE=Release ..
+make -j$[$(nproc)+1]
+strip lib/libzmq.so.*.*
+```
+
+The dynamic library will be outputted in `lib/libzmq.so.*.*`.
+
+### i386
+
+```
+mkdir build_i386
+cd build_i386
+cmake -DWITH_PERF_TOOL=OFF -DZMQ_BUILD_TESTS=OFF -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_FLAGS=-m32 -DCMAKE_CXX_FLAGS=-m32 ..
+make -j$[$(nproc)+1]
+strip lib/libzmq.so.*.*
+```
+
+The dynamic library will be outputted in `lib/libzmq.so.*.*`.