Add shell completions by shtab

[Freed-Wu]

mdformat --print-completion bash | sudo tee /usr/share/bash-completion/completions/mdformat
mdformat --print-completion zsh | sudo tee /usr/share/zsh/site-functions/_mdformat
mdformat --print-completion tcsh | sudo tee /etc/profile.d/mdformat.completion.csh

❯ mdformat --<TAB>
option
--check              do not apply changes to files
--end-of-line        output file line ending mode (default: lf)
--help               show this help message and exit
-h                   show this help message and exit
--number             apply consecutive numbering to ordered lists
--print-completion   print shell completion script
--version            show program's version number and exit
--wrap               paragraph word wrap mode (default: keep)
❯ mdformat --end-of-line <TAB>
end_of_line
crlf  keep  lf

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