S3 enhancements

[deepankardatta]

This was to involve @jmcurran to see if converting part of the library to S3 methods would be worthwhile. Reading around the topic it seems like a good idea. It is something I am not massively familiar with. If you're keen some help would be great.

My main aim of the current package is to make some minor enhancements to the functionality (e.g. allowing identification and handling of non-parametric differences in BA calculation) whilst maintaining compatibility with the current package and the jamovi module.

If you're keen I can add you to the package repository so you can modify as you wish. I'm currently developing on a branch to keep things tidy.