This solves a problem where clang and gcc locate the deleted
version of teardown and async_teardown instead of the overloaded
version. It requires overloads to add `teardown_tag` into the signature
so that the rules for argument dependent lookup can find the
right function. Improve documentation of teardown requirements
The documentation is updated to clearly explain the need for including
<beast/websocket/ssl.hpp> to use SSL streams with WebSocket.
The default implementations of teardown and async_teardown now use
static_assert to alert the user of improper usage, with comments
providing guidance for resolving the error.
When a suspended composed operation is resumed, the operation
now posts to the io_service to get in the correct context. Previously,
invokables resumed in the context of a different completion handler.
* asio_handler_invoke for any resumed invokable will return `true`.
