Closes #10 add function `create_iso8601()` #40

Job	Run time
Validation	0s
Render README	0s
Documentation	0s
Code Style / Code Style	1m 1s
Check / (4.1)	53s
Check / (4.2)	50s
Check / (4.3)	1m 8s
Code Coverage / Test Coverage	1m 12s
Check / (devel)	1m 34s
Lint / Lint	58s
Links / Validate Links	10s
Man Pages / Roxygen	49s
Code Coverage / Generate badge for coverage	5s
	8m 40s

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