Closes #10 add function `create_iso8601()` #41

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Render README	0s
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Code Coverage / Test Coverage	1m 26s
Check / (4.1)	49s
Check / (4.2)	53s
Man Pages / Roxygen	51s
Check / (4.3)	1m 9s
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Check / (devel)	1m 31s
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	8m 56s

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