Since this check for suggestion arguments is in both binaries, we can
move it to the common preflight function.

Clean up other areas now that we moved the function.

Use the new logic from `git-sugpatch` to build a `Config` and run
`apply()` on all suggestion input arguments.

Print usage on `-h` and `--help`.

Store the usage brief on `Config` in order to be able to print it from
multiple places.

Add `Options` to `Config` to allow us to get a usage string from a
`Config` instance, which is where we create `Options`.

Needed to remove the `Debug` derive on `Config` in order to add the
field as `Options` doesn't implement `Debug`.

Replace my test exit code with a real one.

Split this out into a separate function because I want to reuse it in
`git-sugapply`.

Forgot to change this line when I set up the loop over suggestion
arguments. We want to parse the current argument instead of hard-coding
the first one.

Remove unused code.