Optionally use KaTeX for csug and release_notes #110

Job	Run time
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	30m 31s
ci (a6osx, macos-12)	20m 17s
ci (ta6osx, macos-12)	18m 26s
ci (i3le, ubuntu-22.04)	12m 51s
ci (ti3le, ubuntu-22.04)	15m 44s
ci (a6le, ubuntu-22.04)	9m 6s
ci (ta6le, ubuntu-22.04)	12m 1s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 26s
ci (i3nt, windows-2022, vs)	11m 49s
ci (ti3nt, windows-2022, vs)	15m 4s
ci (a6nt, windows-2022, vs)	12m 18s
ci (ta6nt, windows-2022, vs)	15m 6s
ci (ta6nt, windows-2022, gcc)	13m 31s
	3h 15m 10s

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