Document the --no-update option for the merge command.
Add placeholder config for the merge command.
Make sure the working copy is up-to-date before merging.
Document the fact that quick branching isn't enabled by default.
Update the config file.

* Remove the 'exclude' key, and add a comment.
* Alphabetically order the keys, because why not?
Detect outdated config files.
Throw a specific Exception when the config is bad.
Detect and re-throw Exception_InvalidConfig.