asio update - chriskohlhoff/asio

Changed to require C++11 as the minimum language standard.
Removed deprecated functionality from the asio::execution namespace.
Removed deprecated invocation and allocation hooks.
Added compatibility between Asio's placeholders and std::bind.
Added try_send_via_dispatch and try_send_n_via_dispatch functions to
channels.
Improved C++11 support for multi-signature channels.
Fixed compatibility between channel asynchronous operations and
any_completion_handler.
Added missing equality operators for mixed property types belonging to the
same category.
Fixed an issue where spawn-based stackful coroutines would terminate the
program when used with asynchronous operations that have a completion
signature starting with std::exception_ptr.

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