v2.0.0

• Breaking: Async::new() now takes types that implement AsFd/AsSocket instead of AsRawFd/AsRawSocket, in order to implement I/O safety. (#142)
• Breaking: Async::get_mut(), Async::read_with_mut() and Async::write_with_mut() are now unsafe. The underlying source is technically "borrowed" by the polling instance, so moving it out would be unsound. (#142)
• Expose miscellaneous kqueue filters in the os::kqueue module. (#112)
• Expose a way to get the underlying Poller's file descriptor on Unix. (#125)
• Add a new Async::new_nonblocking method to allow users to avoid duplicating an already nonblocking socket. (#159)
• Remove the unused fastrand and memchr dependencies. (#131)
• Use tracing instead of log. (#140)
• Support ESP-IDF. (#144)
• Optimize the block_on function to reduce allocation, leading to a slight performance improvement. (#149)