libev port

merged by andy@warmcat.com via https://github.com/gaby64/libwebsockets-libev

To use, you need to both

 - cmake ---> -DLWS_USE_LIBEV=1

 - info->options must have LWS_SERVER_OPTION_LIBEV set when creating the context

this is so a single library can be built for distros to support apps that use
normal polling and apps that use libev polling.