Merge pull request #435 from zcash/update_visibility #3212

Job	Run time
Book tests	14s
Latest build on ubuntu-latest	52s
Bitrot check	3m 20s
Latest build on windows-latest	2m 19s
Latest build on macOS-latest	43s
Build target wasm32-wasi	2m 44s
Code coverage	9m 26s
Test on ubuntu-latest	9m 26s
Test on windows-latest	10m 20s
Test on macOS-latest	7m 38s
Intra-doc links	3m 28s
Rustfmt	16s
	50m 46s

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