Allow for omitting return types for typed method signatures #267

Job	Run time
Documentation	55s
Julia 1 - macos-latest - x64	1m 47s
Julia nightly - ubuntu-latest - x64	43s
Julia 1 - ubuntu-latest - x64	40s
Julia 1.0 - ubuntu-latest - x64	1m 26s
Julia 1.0 - macos-latest - x64	2m 40s
Julia nightly - macos-latest - x64	1m 34s
Julia nightly - windows-latest - x64	2m 47s
Julia 1.0 - windows-latest - x64	3m 7s
Julia 1 - windows-latest - x64	1m 1s
	16m 40s

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