Add changelog for `0.15.0` #450

Job	Run time
rust_clippy_check_windows	3m 52s
build_static_and_test_ubuntu (release/6.0, nightly, no valgrind)	5m 11s
docs_rs_check	1m 30s
build_dynamic_and_test_windows_pre	6m 7s
build_static_and_test_ubuntu (release/6.0, 1.70.0, no valgrind)	5m 12s
rust_clippy_check_ubuntu	5m 19s
build_static_and_test_ubuntu (release/6.1, nightly, no valgrind)	5m 42s
rustfmt_check (macos-latest)	9s
build_static_and_test_ubuntu (release/6.1, 1.70.0, no valgrind)	5m 23s
rustfmt_check (windows-latest)	36s
build_static_and_test_ubuntu (release/7.0, nightly, valgrind)	43m 29s
rustfmt_check (ubuntu-latest)	5s
build_static_and_test_ubuntu (release/7.0, nightly, no valgrind)	6m 24s
build_static_and_test_ubuntu (release/7.0, 1.70.0, no valgrind)	6m 24s
build_dynamic_and_test_windows (nightly)	2m 42s
build_dynamic_and_test_windows (1.70.0)	1m 46s
	1h 39m 51s

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