Slim installation option or model inference export option

[twoertwein]

rsmtools has many large dependencies. Many of them are not needed at inference time.

It would be nice to either:

1. Use the pip compatible install options like pip install "rsmtools[full]" to install all dependencies only when needed
2. Add a method to export an already trained model so that it can be run without requiring rsmtools (for example as a sklearn pipeline). Ideally it would allow specifying all the options that fast_predict supports.