feat: add --version, completions, manpages

[caarlos0]

not sure how useful completions are in this case... might not be worth adding them... wdyt?

[coveralls]

Pull Request Test Coverage Report for Build 11974746931

Details

• 14 of 20 (70.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.6%) to 89.616%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
main.go	14	20	70.0%
<!--	Total:	14	20	70.0%	-->

Totals
Change from base Build 11974720212:	-0.6%
Covered Lines:	630
Relevant Lines:	703

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💛 - Coveralls

[meowgorithm]

Makes sense to me. Good CLI hygiene.

[bashbunni]

do I need to do anything with the output from sequin man? Also, should this command be included in the help command or is it left out on purpose?