- docs: misc improvements (#2572, #2658, #2663, #2656, #2647, #2630, #2487, #2621,
  #2624, #2600, #2623, #2622, #2577, #2569, #2589, #2575, #2540, #2564, #2567,
  #2520, #2521, #2572, #2493)
- rt: allow calls to `block_on` inside calls to `block_in_place` that are
  themselves inside `block_on` (#2645)
- net: fix non-portable behavior when dropping `TcpStream` `OwnedWriteHalf` (#2597)
- io: improve stack usage by allocating large buffers on directly on the heap
  (#2634)
- io: fix unsound pin projection in `AsyncReadExt::read_buf` and
  `AsyncWriteExt::write_buf` (#2612)
- io: fix unnecessary zeroing for `AsyncRead` implementors (#2525)
- io: Fix `BufReader` not correctly forwarding `poll_write_buf` (#2654)

- coop: returning `Poll::Pending` no longer decrements the task budget (#2549)

- io: little-endian variants of `AsyncReadExt` and `AsyncWriteExt` methods
  (#1915)
- io: fix panic in `AsyncReadExt::read_line` (#2541)
- task: add [`tracing`] instrumentation to spawned tasks (#2655)
- sync: allow unsized types in `Mutex` and `RwLock` (via `default` constructors)
  (#2615)
- net: add `ToSocketAddrs` implementation for `&[SocketAddr]` (#2604)
- fs: add `OpenOptionsExt` for `OpenOptions` (#2515)
- fs: add `DirBuilder` (#2524)

[`tracing`]: https://crates.io/crates/tracing

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

Co-authored-by: Carl Lerche <me@carllerche.com>