Use current-dir as final fallback repo name

It all falls into place! I had been dreading doing this bit, but after
updating the usage guide I realized the CLI args should be split, too.
Which finally means that I can just glue on the PWD name as a final
fallback for the repo name.

Try the args, then the config file(s), then PWD. If nothing works, the
user is in a world of hurt. Bail out.

src/lib.rs

@@ -23,6 +23,8 @@ pub enum Error {
     Placeholder,     // TODO: Enumerate error modes
     MissingGiteaUrl, // the gitea URL wasn't specified on the CLI, env, or config file.
     MissingRepoFRQN, // either the owner, repo, or both weren't specified in the loaded PartialConfig
+    MissingRepoOwner,
+    MissingRepoName,
     WrappedConfigErr(config::Error),
     WrappedReqwestErr(reqwest::Error),
     MissingAuthToken,