Update release notes, etc., for the 1.47.1-rc2 release #100

Job	Run time
Build and test with ASAN enabled	1m 40s
Build and test with gcc	1m 10s
Build and test with clang	1m 14s
Cross-compile for Android (aarch64)	35s
Build and test with gcc -m32	1m 25s
Cross-compile for Android (armv7a)	34s
Build and test on macOS	1m 24s
Build and test with UBSAN enabled	1m 22s
Cross-compile for Android (i686)	36s
Cross-compile for Android (x86_64)	37s
Build mke2fs on Windows with mingw32	2m 19s
Build mke2fs on Windows with mingw64	2m 16s
	15m 12s

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