Add SHE doxygen so documentation can pick up the API and notes. #6563

Job	Run time
build library (--enable-smallstack --disable-asm --enable-cryptonly --enable-all-crypto --disable...	1m 8s
build library (--enable-cryptonly --enable-all-crypto --disable-examples --disable-benchmark --di...	1m 7s
build library (--disable-asm --enable-cryptonly --enable-all-crypto --disable-examples --disable-...	1m 7s
build library (--enable-cryptonly --enable-all-crypto --disable-examples --disable-benchmark --di...	1m 14s
build library (--disable-intelasm --enable-cryptonly --enable-all-crypto --disable-examples --dis...	59s
build library (--enable-cryptonly --enable-all-crypto --disable-examples --disable-benchmark --di...	1m 20s
build library (--disable-intelasm --enable-cryptonly --enable-all-crypto --disable-examples --dis...	58s
build library (--enable-intelasm --enable-cryptonly --enable-all-crypto --disable-examples --disa...	1m 8s
build library (--enable-smallstack --enable-cryptonly --enable-all-crypto --disable-examples --di...	1m 4s
build library (--enable-smallstack --enable-intelasm --enable-cryptonly --enable-all-crypto --dis...	57s
build library (--enable-cryptonly --enable-all-crypto --disable-examples --disable-benchmark --di...	1m 7s
	12m 9s

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