Add explicit error messages for boolean functions #29

Job	Run time
Documentation	2m 13s
Julia 1.8 - ubuntu-latest - x64 - push	2m 46s
Julia 1.8 - ubuntu-latest - x86 - push	4m 5s
Julia 1.8 - macOS-latest - x64 - push	4m 4s
Julia 1.8 - windows-latest - x64 - push	12m 52s
Julia 1.8 - windows-latest - x86 - push	4m 1s
Julia 1 - ubuntu-latest - x64 - push	2m 34s
Julia 1 - ubuntu-latest - x86 - push	4m 57s
Julia 1 - macOS-latest - x64 - push	2m 58s
Julia 1 - windows-latest - x64 - push	5m 29s
Julia 1 - windows-latest - x86 - push	3m 49s
Julia nightly - ubuntu-latest - x64 - push	2m 57s
Julia nightly - ubuntu-latest - x86 - push	5m 11s
Julia nightly - macOS-latest - x64 - push	4m 51s
Julia nightly - windows-latest - x64 - push	6m 24s
Julia nightly - windows-latest - x86 - push	4m 33s
	1h 13m 44s

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