Add methods for calling multi-response gaussian family #46

Job	Run time
Julia 1.6 - ubuntu-latest - x64	3m 16s
Julia 1.6 - macOS-latest - x64	5m 20s
Julia 1.6 - windows-latest - x64	10m 45s
Julia 1 - ubuntu-latest - x64	5m 14s
Julia 1 - macOS-latest - x64	4m 12s
Julia 1 - windows-latest - x64	8m 54s
Julia nightly - ubuntu-latest - x64	3m 10s
Julia nightly - macOS-latest - x64	7m 40s
Julia nightly - windows-latest - x64	8m 53s
	57m 24s

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