git ship [<branchname>] 

Allow git ship to take in an optional branch name.
Separated the git ship tests so this could be thoroughly tested.
I would think that could be intuitively figured out. 
I dislike how we are showing the commands here and favor the man page styles to avoid repetition.

```
git ship [<branchname>] [-m <message>]
git ship --abort
```

And then explain the options