Building under macOS

The library compiles and runs all tests under macOS High Sierra (OS X).

I have fetched the dependencies with brew

 brew install openssl boost zlib

My automated integration system use these commands to build the library and run the tests (from the root of the cloned git repository):

rm -rf build
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release -DOPENSSL_ROOT_DIR=/usr/local/opt/openssl -DOPENSSL_LIBRARIES=/usr/local/opt/openssl/lib -DBOOST_LIBRARIES=/usr/local/opt/boost/lib -DBOOSTL_ROOT_DIR=/usr/local/opt/boost -DZLIB_INCLUDE_DIRS=/usr/local/opt/zlib/include/ -DZLIB_LIBRARIES=/usr/local/opt/zlib/lib/ .. 
make -j4
ctest