CI/CD workflow using GitHub Actions is added. #2

Job	Run time
Build Antimony on macos-11-release	9m 22s
Build Antimony on macos-11-debug	8m 54s
Build Antimony on macos-latest-release	1m 22s
Build Antimony on macos-latest-debug	1m 7s
Build Antimony on ubuntu-latest-release	3m 42s
Build Antimony on ubuntu-latest-debug	2m 21s
Build Antimony on windows-latest-release	3m 58s
Build Antimony on windows-latest-debug	3m 13s
Build Antimony on manylinux2014-release	14m 51s
Build Antimony on manylinux2014-debug	14m 15s
	1h 3m 5s

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