Honour the git-authors plugin's setting to render the authors' names
as links pointing to their email address:
* If the git-authors plugin is enabled and its show_email_address
option is not set, or is set to true, render the author's name as a
"mailto:" link.
* If the git-authors plugin is enabled and its show_email_address
option is set to false, render the author's name in plain text with
no link.
* If the git-authors plugin is not enabled (or not installed), don't
show author information.
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