Add support for Cygwin #339

Job	Run time
Style/format	17s
Style/spellcheck	6s
Build/Test (ubuntu-latest)	23s
Code Coverage (ubuntu-latest)	1m 56s
Code Coverage (macos-latest)	1m 55s
Style/lint (windows-latest)	1m 15s
Build/Test (macos-latest)	36s
Build/Test (windows-latest)	1m 0s
Style/lint (macos-latest)	33s
Code Coverage (windows-latest)	3m 28s
Style/lint (ubuntu-latest)	33s
	12m 2s

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