systemd::journal doesn't return Result

[cglong]

We were looking at using systemd::journal for sending messages to journald, but noticed all the functions either return a c_int or nothing at all. Given the c_int values aren't well-defined in the docs, we essentially have no way of knowing whether the message was successfully sent or not.

Could these functions be updated to instead return a Result or, less ideally, could the docs be updated to include details on how to interpret the c_ints? Thank you!

[codyps]

I agree that these should return a Result type instead of a plain c_int. Would happily take a patch to do this.