While necessary as part of this change, it seems unfortunate that all callers need to explicitly pass in the comment char all the time. Especially as this can be configured in `core.commentchar`, it seems that there should be a way to just use libgit2's default comment char (either '#' or have it read an override from the config settings).

Another thought - is a byte sufficient? Couldn't this be any UTF-8 char?

/cc @carlosmn