subscriber: prepare to release v0.3.16

[hawkw]

0.3.16 (October 6, 2022)

This release of tracing-subscriber fixes a regression introduced in
v0.3.15 where Option::None's Layer
implementation would set the max level hint to OFF. In addition, it
adds several new APIs, including the Filter::event_enabled method for
filtering events based on fields values, and the ability to log internal
errors that occur when writing a log line.

This release also replaces the dependency on the unmaintained
[ansi-term] crate with the [nu-ansi-term] crate, resolving an
informational security advisory (RUSTSEC-2021-0139 for
[ansi-term]'s maintainance status. This increases the minimum
supported Rust version (MSRV) to Rust 1.50+, although the crate should
still compile for the previous MSRV of Rust 1.49+ when the ansi
feature is not enabled.

Fixed

• layer: Option::None's Layer impl always setting the
  max_level_hint to LevelFilter::OFF (ensure the None-layer doesn't override the max-level erroneously #2321)
• Compilation with -Z minimal versions (fix minimal-versions correctness (v0.1.x) #2246)
• env-filter: Clarify that disabled level warnings are emitted by
  tracing-subscriber (disabled level warning: say which create the message refers to #2285)

Added

• fmt: Log internal errors to stderr if writing a log line fails
  (subscriber: if error occurs when formatting event, write error to Writer #2102)
• fmt: FmtLayer::log_internal_errors and
  FmtSubscriber::log_internal_errors methods for configuring whether
  internal writer errors are printed to stderr (subscriber: if error occurs when formatting event, write error to Writer #2102)
• fmt: #[must_use] attributes on builders to warn if a
  Subscriber is configured but not set as the default subscriber
  (feat: mark builders as must_use #2239)
• filter: Filter::event_enabled method for filtering an event
  based on its fields (Add Filter::event_enabled #2245, Clarify filter.not() w.r.t. event_enabled #2251)
• filter: Targets::default_level accessor (Add a method to Targets to get the default level #2242)

Changed

• ansi: Replaced dependency on unmaintained ansi-term crate with
  nu-ansi-term ((deps: Use nu-ansi-term to replace unmaintained ansi_term #2287, fixes informational advisory
  RUSTSEC-2021-0139)
• tracing-core: updated to 0.1.30
• Minimum Supported Rust Version (MSRV) increased to Rust 1.50+ (when
  the ansi) feature flag is enabled (deps: Use nu-ansi-term to replace unmaintained ansi_term #2287)

Documented

• fmt: Correct inaccuracies in fmt::init documentation (tracing-subscriber: correct fmt::init() documentation #2224)
• filter: Fix incorrect doc link in filter::Not combinator
  (Not is not, not or #2249)

Thanks to new contributors @cgbur, @DesmondWillowbrook, @RalfJung, and
@poliorcetics, as well as returning contributors @CAD97, @connec,
@jswrenn, @guswynn, and @bryangarza, for contributing to this release!