message: docs: fix a few typos
diff: //! entered, exited, and closed. Since these additional span lifecycle logs have
  //! the potential to be very verbose, and don't include additional fields, they
  //! will always be emitted at the `Trace` level, rather than inheriting the
  -//! level of the span that generated them. Furthermore, they are are categorized
  +//! level of the span that generated them. Furthermore, they are categorized
  //! under a separate `log` target, "tracing::span" (and its sub-target,
  //! "tracing::span::active", for the logs on entering and exiting a span), which
  //! may be enabled or disabled separately from other `log` records emitted by
  //! crate, allowing spans to be attached to `Future`s, `Stream`s, and `Executor`s.
  //! - [`tracing-subscriber`] provides `tracing_subscriber::Subscribe` implementations and
  //! utilities for working with collectors. This includes a [`FmtSubscriber`]
  -//! `FmtSubscriber` for logging formatted trace data to stdout, with similar
  +//! for logging formatted trace data to stdout, with similar
  //! filtering and formatting to the [`env_logger`] crate.
  //! - [`tracing-log`] provides a compatibility layer with the [`log`] crate,
  //! allowing log messages to be recorded as `tracing` `Event`s within the
  