MaG21

I managed to compile the code with xcode. Clang doesn't fully support C++17, however the following expression resolves to true when compiling with clang `__cplusplus >= 201703L`, which prevents us...

``` $ luarocks remove lua-cjson $ luarocks install lua-cjson 2.1.0-1 ```

@atipugin still, people will benefit more if `#listen` has more sensible defaults.

Hello, is it possible that we can merge this PR in a new Swift 4 feature branch ?