Variable length key support. #365

Job	Run time
build (clang 11 Release, Release, clang, 11)	19m 38s
build (clang 11 Release with ASan, Release, ON, clang, 11)	21m 52s
build (clang 11 Release with TSan, Release, ON, clang, 11)	20m 42s
build (clang 11 Release with UBSan, Release, ON, clang, 11)	21m 36s
build (clang 11 Debug, Debug, clang, 11)	18m 55s
build (clang 11 Debug with ASan, Debug, ON, clang, 11)	20m 11s
build (clang 11 Debug with TSan, Debug, ON, clang, 11)	19m 7s
build (clang 11 Debug with UBSan, Debug, ON, clang, 11)	20m 8s
build (clang 12 Release, Release, clang, 12)	23m 53s
build (clang 12 Release with ASan, Release, ON, clang, 12)	24m 12s
build (clang 12 Release with TSan, Release, ON, clang, 12)	22m 22s
build (clang 12 Release with UBSan, Release, ON, clang, 12)	22m 4s
build (clang 12 Debug, Debug, clang, 12)	20m 15s
build (clang 12 Debug with ASan, Debug, ON, clang, 12)	20m 43s
build (clang 12 Debug with TSan, Debug, ON, clang, 12)	18m 49s
build (clang 12 Debug with UBSan, Debug, ON, clang, 12)	19m 24s
build (GCC 10 Release, Release, gcc, 10)	12m 2s
build (GCC 10 Release with ASan, Release, ON, gcc, 10)	17m 58s
build (GCC 10 Release with TSan, Release, ON, gcc, 10)	13m 30s
build (GCC 10 Release with UBSan, Release, ON, gcc, 10)	15m 37s
build (GCC 10 Debug, Debug, gcc, 10)	13m 27s
build (GCC 10 Debug with ASan, Debug, ON, gcc, 10)	14m 33s
build (GCC 10 Debug with TSan, Debug, ON, gcc, 10)	15m 8s
build (GCC 10 Debug with UBSan, Debug, ON, gcc, 10)	13m 7s
	7h 29m 13s

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