* app().registerHttpHandler() accepts coroutine as handlers
* HttpController can use coroutine as handlers'
* Http request handlers with coroutine catches exception instead of crashing the entire app
* DbClient now has execSqlCoro that is awaitable
* DbClient now has newTransactionCoro that is awaitable
* HttpClient have awaitable sendRequestCoro
* WebSocketClient have awaitable connectToServerCoro
* WebSocketClient have setAsyncMessageHandler and setAsyncConnectionClosedHandler
* drogon::AsyncTask and drogon::Task<T> as our corutine types
* Related tests
* Misc
Future work
* Coroutine for WebSocket server
* Known issues
co_future() and sync_wait may crash. It looks like GCC bug but I'm not sure.
Workarround: Make an coroutine of AsyncTask. Then launch said coroutine.
Not sure why wrapping the exact same thing in function crashes things.
Co-authored-by: an-tao <antao2002@gmail.com>
