Major changes

• Decoupled tokio, which is now an optional dependency. futures utilities,
  like channels, are used instead. stdio module still requires an async
  executor to work. See its documentations for the the usage with tokio or
  async-io driver, briefly lock_tokio() or async_io::Async::new(lock()).

• Frontend is renamed to MainLoop, and a run_buffered shortcut is
  provided to auto-wrap non-AsyncBufRead arguments with a buffer.

• LspService::{Error,Response} type bounds are relaxed. (#5) Users are free
  to implement different error and/or response types in their middlewares. But
  they should still meet the bounds on MainLoop constructors.

Features

• Separated Error::Eof from Error::Io.

• {Server,Client}Socket::new_closed constructor for testing.

• AnyEvent::{is,downcast_{ref,mut}} to in sync with Box<dyn Any>.

• More examples, tests and benchmarks.

• Complete documentations.

Internal changes

• The platform related behavior of ClientProcessMonitor is moved into an
  individual crate waitpid-any. It now has a blocking implementation and
  spawns a thread. *NIX, Windows and *BSD are all supported now.

• Writing outgoing messages is now done concurrently and will not suspend
  reading and request handling.