Signature default encoding?

[bors-ltd]

Hi,

It's not documented but it seems the default encoding for the signature name is ASCII: https://github.com/libgit2/pygit2/blob/master/src/signature.c#L41

Is there a particular reason why it's not UTF-8, like about everything else in git/libgit2?

When I pass a unicode/text object, I wouldn't expect to provide the encoding as well (there is an accent in my name).

Especially when it seems to be the default for internally built signatures: https://github.com/libgit2/pygit2/blob/master/src/signature.c#L114