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@charlierudolph this implements #87 
Currently we have a `create_feature_branch` function. I believe the should be extended to the following

```bash
function create_and_checkout_branch {
  local new_branch_name=$1
  local parent_branch_name=$2
  run_command "git checkout -b $new_branch_name $parent_branch_name"
}

function create_and_checkout_feature_branch {
  create_and_checkout_branch $1 $main_branch_name  
}
```

That way the last two lines could become
```bash
add_to_undo_script "create_and_checkout_branch $initial_branch_name $current_sha"
```