Update release notes [ci skip]

RELEASES.md

@@ -10,14 +10,15 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Numerous new test cases for existing features.
 
 ### Changed
-- Replace Boost.Test with Boost.LightweightTest as the only test framework used in GIL ([PR #459](https://github.com/boostorg/gil/pull/459) and [PR #464](https://github.com/boostorg/gil/pull/464)).
+- Replace Boost.Test with Boost.LightweightTest as the only test framework used in GIL ([PR #459](https://github.com/boostorg/gil/pull/459) and [PR #464](https://github.com/boostorg/gil/pull/464)). This also restructured the `test/extension/io/` sub-tree and targets in related `Jamfile`-s.
 - Removed remaining uses of Boost.MPL ([PR #441](https://github.com/boostorg/gil/pull/441) and ).
 - Renamed all macros using `BOOST_GIL_` prefix ([PR #411](https://github.com/boostorg/gil/pull/411)).
 - Renamed all CMake configuration options using `BOOST_GIL_` prefix ([PR #419](https://github.com/boostorg/gil/pull/419)).
 
 ### Removed
 - Removed `extension/dynamic_image/reduce.hpp` as unused and possibly unfinished ([PR #466](https://github.com/boostorg/gil/pull/466)). An implementation attempt of techniques described in the paper [Efficient Run-Time Dispatching in Generic Programming with Minimal Code Bloat](http://lubomir.org/academic/MinimizingCodeBloat.pdf) by Lubomir Bourdev, Jaakko Jarvi.
 - Removed dependency on Boost.MPL, Boost.System and Boost.Test.
+- Started removing public macros for compile-time configuration of I/O extension tests, i.e. `BOOST_GIL_IO_TEST_ALLOW_READING_IMAGES` and `BOOST_GIL_IO_TEST_ALLOW_WRITING_IMAGES`. Instead, if a test target is built, it builds all its test cases unconditionally.
 
 ### Fixed
 - Avoid `longjmp` interaction during destruction of I/O extension objects ([PR #433](https://github.com/boostorg/gil/pull/433)).