[FEATURE] respect .mailmap

[lukehsiao]

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When cog generates a changelog and grabs author names, it appears to ignore the mappings defined in .mailmap: https://git-scm.com/docs/gitmailmap

So, if an author is, for example, Typo <email@example.com>, and the .mailmap corrects this to First Last <email@example.com>, cog changelog will attribute the commit to Typo.

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Respect .mailmap for name mappings.

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