Fails to build: Boost >=1.70.0 has removed boost/asio/handler_type.hpp

[abgault]

Boost has deprecated the handler_type with the note "(Deprecated: Use two-parameter version of async_result.)".

Build output:

In file included from /dev/pusher-cpp/pusher++/examples/server.cpp:6:
/dev/pusher-cpp/pusher++/include/pusher++/server.hpp:14:10: fatal error: 'boost/asio/handler_type.hpp' file not found
#include <boost/asio/handler_type.hpp>

In file included from /dev/pusher-cpp/pusher++/test/test_coroutine.cpp:11:
/dev/pusher-cpp/pusher++/include/pusher++/client.hpp:12:10: fatal error: 'boost/asio/handler_type.hpp' file not found
#include <boost/asio/handler_type.hpp>
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In file included from /dev/pusher-cpp/pusher++/examples/client.cpp:7:
/dev/pusher-cpp/pusher++/include/pusher++/client.hpp:12:10: fatal error: 'boost/asio/handler_type.hpp' file not found
#include <boost/asio/handler_type.hpp>
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In file included from /dev/pusher-cpp/pusher++/test/test_signal_filter.cpp:14:
/dev/pusher-cpp/pusher++/include/pusher++/client.hpp:12:10: fatal error: 'boost/asio/handler_type.hpp' file not found
#include <boost/asio/handler_type.hpp>