Added the ability to detect the executor call stack and whether we're
running from an initiating function or not.
Integration tests now consistently check these two.
Fixed a potential ODR violation with `asio::coroutine` under MSVC, manifesting as sporadic test failures under release configurations.
`any_stream` has been replaced by the internal `EngineStream` concept
and the `engine` interface.
`algo_runner` has been replaced by `top_level_algo`, improving algorithm
type-erasing
This change is required by #195 and beneficial for #75close#259
Separate compilation
Immediate completions are now posted through the I/O executor
Jamfiles now correctly requires C++11
Refactored the protocol and channel modules
Removed example on default completion tokens
close#23close#112
