Release v0.10.0

Asio completion token support and thread-safe Session operations.

New features:

• Callback functions, yield_context, use_awaitable, and use_future now supported as completion tokens.
• C++20 coroutines now supported
• Migrated from AsyncResult to new ErrorOr class which better emulates the proposed std::expected.
• Session's asynchonous operations now return an ErrorOr result when passed a yield_context as the completion token.
• Added Session overloads with the ThreadSafe tag type which can be called concurrently by multiple threads.
• Added Realm::captureAbort.
• Session's setWarningHandler, setTraceHandler, setStateChangeHandler, and setChallengeHandler now take effect immediately even when connected.
• Users can bind custom executors to their handlers and Session will use them when executing those handlers.
• Boost.Asio cancellation slot support for Session::call.
• Added Rpc::withCancelMode which specifies the cancel mode to use when triggered by Asio cancellation slots.
• Added withArgsTuple, convertToTuple and moveToTuple to Payload class.
• Added the Deferment tag type (with deferment constexpr variable) to more conveniently return a deferred Outcome` from an RPC handler.