Investigate adding in additional annotations

Right now, tinybaker has only one annotation, e.g. `fileset::`. We might want to leverage the idea to help with interface stuff.

Potential things!
`pkl::`
`json::`
`xml::`
`pd::`

Enabling things like:

```py
def script(self):
self.input_files["model"].predict(self.input_files["data"])
self.output_files['model'] = lololol
```

i'm not sure what the final endpoint of this will be, but it'll be good to start thinking about it. Might inform future API work too.