chore: prepare Tokio v1.21.0

[Darksonn]

1.21.0 (September 2, 2022)

This release is the first release of Tokio to intentionally support WASM. The sync,macros,io-util,rt,time features are stabilized on WASM. Additionally the wasm32-wasi target is given unstable support for the net feature.

Added

• net: add device and bind_device methods to TCP/UDP sockets (#4882)
• net: add tos and set_tos methods to TCP and UDP sockets (#4877)
• net: add security flags to named pipe ServerOptions (#4845)
• signal: add more windows signal handlers (#4924)
• sync: add mpsc::Sender::max_capacity method (#4904)
• sync: implement Weak version of mpsc::Sender (#4595)
• task: add LocalSet::enter (#4765)
• task: stabilize JoinSet and AbortHandle (#4920)
• tokio: add track_caller to public APIs (#4805, #4848, #4852)
• wasm: initial support for wasm32-wasi target (#4716)

Fixed

• miri: improve miri compatibility by avoiding temporary references in linked_list::Link impls (#4841)
• signal: don't register write interest on signal pipe (#4898)
• sync: add #[must_use] to lock guards (#4886)
• sync: fix hang when calling recv on closed and reopened broadcast channel (#4867)
• task: propagate attributes on task-locals (#4837)

Changed

• fs: change panic to error in File::start_seek (#4897)
• io: reduce syscalls in poll_read (#4840)
• process: use blocking threadpool for child stdio I/O (#4824)
• signal: make SignalKind methods const (#4956)

Internal changes

• rt: extract basic_scheduler::Config (#4935)
• rt: move I/O driver into runtime module (#4942)
• rt: rename internal scheduler types (#4945)

Documented

• chore: fix typos and grammar (#4858, #4894, #4928)
• io: fix typo in AsyncSeekExt::rewind docs (#4893)
• net: add documentation to try_read() for zero-length buffers (#4937)
• runtime: remove incorrect panic section for Builder::worker_threads (#4849)
• sync: doc of watch::Sender::send improved (#4959)
• task: add cancel safety docs to JoinHandle (#4901)
• task: expand on cancellation of spawn_blocking (#4811)
• time: clarify that the first tick of Interval::tick happens immediately (#4951)

Unstable

• rt: add unstable option to disable the LIFO slot (#4936)
• task: fix incorrect signature in Builder::spawn_on (#4953)
• task: make task::Builder::spawn* methods fallible (#4823)