Add SHE doxygen so documentation can pick up the API and notes. #2838

Job	Run time
make check (--enable-wolfEntropy --enable-smallstackcache --enable-smallstack --enable-all CFLAGS...	3m 59s
make check (--disable-asm --enable-wolfEntropy --enable-smallstackcache --enable-smallstack --ena...	4m 41s
make check (--enable-all --enable-debug-trace-errcodes CFLAGS="-DWC_RNG_SEED_CB -DWOLFSSL_TRACK_M...	2m 51s
make check (--enable-amdrand --enable-smallstackcache --enable-smallstack --enable-all CFLAGS="-D...	2m 51s
make check (--enable-smallstack --enable-all CFLAGS="-DWC_RNG_SEED_CB -DWOLFSSL_TRACK_MEMORY -DW...	2m 57s
make check (--enable-intelrdseed --enable-smallstackcache --enable-smallstack --enable-all CFLAGS...	2m 29s
make check (--enable-smallstackcache --enable-smallstack --enable-all --enable-debug-trace-errcod...	3m 1s
	22m 49s

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