Can additional arguments be passed to command?

Hi,

I was wondering if it's possible to have additional arguments to the general commands? I'm already running my tests with a custom config file:
```
backstop reference --config=main
```
The reason is that I want to have multiple helper files and I want to use the additional argument to determine which helper files to require. This way I can test multiple different applications since each of the helper files contain the URLs and endpoints for Backstop to visit.

Any ideas/pointers on how this can be accomplished?

Thanks

Start by tracing the command parsing for `backstop reference --config=main` and how the custom config and helper files are loaded. Determine whether an additional argument can be defined and propagated to the helper-file selection, then verify the supported invocation and document or test the resulting behavior.

Written by the indexing model from the issue text.