Update release notes, etc., for the 1.47.1-rc1 release #90

Job	Run time
Build and test with clang	1m 22s
Build and test with ASAN enabled	1m 44s
Build and test with gcc	1m 11s
Cross-compile for Android (aarch64)	44s
Cross-compile for Android (armv7a)	35s
Build and test with gcc -m32	1m 12s
Cross-compile for Android (i686)	38s
Build and test with UBSAN enabled	1m 24s
Build and test on macOS	1m 23s
Build mke2fs on Windows with mingw32	2m 31s
Cross-compile for Android (x86_64)	51s
Build mke2fs on Windows with mingw64	2m 20s
	15m 55s

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