Merge pull request #492 from rust-lang/KodrAus-patch-2

Update changelog for 0.4.15 with last minute additions

CHANGELOG.md

@@ -6,13 +6,16 @@
 
 * Silence a warning about the deprecated `spin_loop_hint`.
 * Relax ordering in the atomic `set_max_level` call.
+* Add thumbv4t-none-eabi to targets that don't support atomics
 * Allow levels to be iterated over.
 * Implement `Log` on some common wrapper types.
 * Improvements to test coverage.
 * Improvements to documentation.
 * Add key-value support to the `log!` macros.
 * Tighten `kv_unstable` internal dependencies so they don't bump past their current alpha.
 * Add a simple visit API to `kv_unstable`.
+* Support `NonZero*` integers as values in structured logging
+* Support static strings as keys in structured logging
 
 ## [0.4.14] - 2021-01-27