v.0.6.15

[eao197]

This is a maintenance release.

A fix for CMake script for case when RESTINIO_FIND_DEPS=ON and RESTINIO_FMT_HEADER_ONLY=OFF (#159).

Usage of std::aligned_storage_t in implementation of writable_item_t has been removed (it's deprecated in C++23).

In some places std::launder is used (if available) to avoid UB accessing a pointer after placement new.

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This discussion was created from the release v.0.6.15.